docker-agent: single-source docs via Hugo module mount (#25480)

Single-sources the Docker Agent documentation from the product repo via
a Hugo module mount, joining the pattern used by CLI, Buildx, Compose,
BuildKit, Model Runner, and the Moby API. Closes the docs.docker.com
side of docker/docker-agent#3371.

## Context

The pages under `content/manuals/ai/docker-agent/` were hand-authored
duplicates of the product repo docs and drifted on every upstream
change. The source docs were converted to portable Hugo-clean Markdown
and prepared for mounting in docker/docker-agent#3413 and
docker/docker-agent#3414, released in docker-agent v1.96.0.

## What changed

| Change | Detail |
|---|---|
| `go.mod` | `github.com/docker/docker-agent v1.96.0` added to `require`
and `tool` |
| `hugo.yaml` | `module.imports` mounts the eight docs sections and
`demo.gif` onto `content/manuals/ai/docker-agent/` |
| Content | The 16 hand-authored pages are removed; `_index.md` stays
hand-authored (landing page), with links rewritten to the mounted pages
|
| `_vendor/` | 99 vendored files from the module |
| `.github/workflows/sync-docker-agent-docs.yml` | Daily poll that
vendors the latest docker-agent release and opens a bot PR, modeled on
`sync-cli-docs.yml` |

## URL preservation

Every removed page keeps its URL: the mounted pages carry `aliases`
front matter (added upstream in docker/docker-agent#3414), and
`_index.md` keeps aliases for the removed section indexes
(`integrations/`, `reference/`, `reference/examples/`).

| Old URL | Redirects to |
|---|---|
| `/ai/docker-agent/tutorial/` | `.../getting-started/quickstart/` |
| `/ai/docker-agent/best-practices/` | `.../guides/tips/` |
| `/ai/docker-agent/evals/` | `.../features/evaluation/` |
| `/ai/docker-agent/local-models/` | `.../providers/local/` |
| `/ai/docker-agent/model-providers/` | `.../providers/overview/` |
| `/ai/docker-agent/rag/` | `.../tools/rag/` |
| `/ai/docker-agent/sharing-agents/` | `.../concepts/distribution/` |
| `/ai/docker-agent/integrations/{a2a,acp,mcp}/` | `.../features/a2a/`,
`.../features/acp/`, `.../tools/mcp/` |
| `/ai/docker-agent/reference/{cli,config,toolsets}/` |
`.../features/cli/`, `.../configuration/overview/`,
`.../configuration/tools/` |
| `/ai/docker-agent/integrations/`, `/ai/docker-agent/reference/`,
`/ai/docker-agent/reference/examples/` | `/ai/docker-agent/` |

## Mount scope

All eight sections are mounted rather than a core subset:
`refLinksErrorLevel: ERROR` makes partial mounts fail the build for any
relative link into an unmounted page, and the link closure from the core
sections already pulls in 68 of the 90 pages. Mounting everything keeps
the build link-safe and removes all drift.

## Keeping the pin fresh

On each docker-agent release, `sync-docker-agent-docs.yml` (daily poll,
mirrors `sync-cli-docs.yml`) compares the latest release tag against the
pinned version and opens a bot PR with the re-vendored module.
docker/docker-agent also runs `validate-upstream.yml` on every docs PR,
so upstream changes that would break this site fail CI before they merge
(two source-side issues were caught exactly this way while preparing
this change).

## Validation

`docker buildx bake validate` passes on this branch:

| Target | Result |
|---|---|
| test (Hugo build + htmltest) | pass (3196 pages, 1515 aliases, 3110
documents tested) |
| lint | pass |
| unused-media | pass |
| test-go-redirects | pass |
| validate-vendor | pass |
| dockerfile-lint | pass |

`actionlint` passes on the new workflow.

Author: Sayt-0

.github/workflows/sync-docker-agent-docs.yml

@@ -0,0 +1,130 @@
+name: sync-docker-agent-docs
+
+on:
+  schedule:
+    # Run daily at 02:30 UTC, offset from sync-cli-docs
+    - cron: '30 2 * * *'
+  workflow_dispatch:
+    inputs:
+      version:
+        description: "(optional) docker-agent version - defaults to the latest release tag"
+        required: false
+        default: ""
+  pull_request:
+    paths:
+      - '.github/workflows/sync-docker-agent-docs.yml'
+
+permissions:
+  contents: write
+  pull-requests: write
+
+env:
+  BRANCH_NAME: "bot/sync-docker-agent-docs"
+  MODULE_NAME: "github.com/docker/docker-agent"
+
+jobs:
+  sync-docker-agent-docs:
+    runs-on: ubuntu-24.04
+    steps:
+      -
+        name: Checkout docs repo
+        uses: actions/checkout@93cb6efe18208431cddfb8368fd83d5badbf9bfd # v5
+        with:
+          fetch-depth: 0
+      -
+        name: Get target version
+        id: get-version
+        env:
+          GH_TOKEN: ${{ github.token }}
+        run: |
+          if [ -n "${{ inputs.version }}" ]; then
+            VERSION="${{ inputs.version }}"
+          else
+            VERSION=$(gh release view --repo docker/docker-agent --json tagName --jq .tagName)
+          fi
+          CURRENT=$(go list -m -f '{{ .Version }}' "$MODULE_NAME" || true)
+
+          echo "version=$VERSION" >> "$GITHUB_OUTPUT"
+          echo "current=$CURRENT" >> "$GITHUB_OUTPUT"
+          echo "docker-agent version: **$VERSION** (currently pinned: **$CURRENT**)" | tee -a "$GITHUB_STEP_SUMMARY"
+      -
+        name: Set up Docker Buildx
+        if: steps.get-version.outputs.version != steps.get-version.outputs.current
+        uses: docker/setup-buildx-action@4d04d5d9486b7bd6fa91e7baf45bbb4f8b9deedd # v4
+      -
+        # go mod edit sets the version before plain make vendor: passing
+        # VENDOR_MODULE would run hugo mod get, which records docker-agent's
+        # full transitive graph as indirect requires in go.mod.
+        name: Update vendor
+        if: steps.get-version.outputs.version != steps.get-version.outputs.current
+        run: |
+          go mod edit -require "${MODULE_NAME}@${{ steps.get-version.outputs.version }}"
+          make vendor
+      -
+        name: Detect changes
+        id: changes
+        if: steps.get-version.outputs.version != steps.get-version.outputs.current
+        run: |
+          if [ -n "$(git status --porcelain)" ]; then
+            echo "changes=true" >> "$GITHUB_OUTPUT"
+            echo "Changes detected - syncing Docker Agent docs" >> "$GITHUB_STEP_SUMMARY"
+          else
+            echo "changes=false" >> "$GITHUB_OUTPUT"
+            echo "No changes to sync - Docker Agent docs are up to date" >> "$GITHUB_STEP_SUMMARY"
+          fi
+      -
+        name: Commit changes
+        if: steps.changes.outputs.changes == 'true'
+        env:
+          BRANCH_NAME: ${{ env.BRANCH_NAME }}
+          VERSION: ${{ steps.get-version.outputs.version }}
+        run: |
+          git checkout -b "$BRANCH_NAME"
+          git config user.name "github-actions[bot]"
+          git config user.email "41898282+github-actions[bot]@users.noreply.github.com"
+          git add -A
+          git commit -m "docker-agent: sync docs with docker-agent $VERSION"
+      -
+        name: Create or update Pull Request
+        if: steps.changes.outputs.changes == 'true' && github.event_name != 'pull_request'
+        env:
+          GH_TOKEN: ${{ github.token }}
+          BRANCH_NAME: ${{ env.BRANCH_NAME }}
+          PR_TITLE: "docker-agent: sync docs with docker-agent ${{ steps.get-version.outputs.version }}"
+          PR_BODY: |
+            ## Summary
+
+            Automated sync of Docker Agent documentation from the docker/docker-agent repository.
+
+            **docker-agent version:** ${{ steps.get-version.outputs.version }}
+
+            ---
+
+            > [!IMPORTANT]
+            > **Reviewer:** Please close and reopen this PR to trigger CI checks.
+            > See: https://docs.github.com/en/actions/how-tos/write-workflows/choose-when-workflows-run/trigger-a-workflow#triggering-a-workflow-from-a-workflow
+        run: |
+          # Check for existing open PR from this branch
+          EXISTING_PR=$(gh pr list --state open --head "$BRANCH_NAME" --json url --jq ".[0].url // empty")
+
+          if [ -n "$EXISTING_PR" ]; then
+            echo "Updating existing PR: $EXISTING_PR" >> "$GITHUB_STEP_SUMMARY"
+            git push -u origin "$BRANCH_NAME" --force
+            gh pr edit "$EXISTING_PR" --title "$PR_TITLE" --body "$PR_BODY"
+          else
+            # Check if a closed PR with the same title already exists
+            CLOSED_PR=$(gh pr list --state closed --search "$PR_TITLE in:title" --json url --jq ".[0].url // empty")
+            if [ -n "$CLOSED_PR" ]; then
+              echo "A closed PR already exists for this version: $CLOSED_PR" >> "$GITHUB_STEP_SUMMARY"
+              echo "Skipping PR creation."
+              exit 0
+            fi
+
+            echo "Creating new PR" >> "$GITHUB_STEP_SUMMARY"
+            git push -u origin "$BRANCH_NAME"
+            gh pr create \
+              --title "$PR_TITLE" \
+              --body "$PR_BODY" \
+              --base main \
+              --head "$BRANCH_NAME"
+          fi