[scottzx]

Summary

Remove the deprecated Feature Blueprint UI, settings, service/types, API routes, CLI/MCP commands, and feature-to-task write paths. Ordinary tasks, milestones, and Gantt schedules continue to work; old view/group preferences fall back to supported task views.

Retain historical blueprint database tables, data, and schema reconciliation. Update active PM guidance and product documentation, and label the original feature documents as historical.

Scope

Only the retirement-related paths are included (76 paths, 75 file changes with one schema-test rename). ACP Workbench, task hierarchy, and all submodule pointers remain excluded. The shared working tree was not modified while preparing this PR.

The pre-existing frontend CI baseline was fixed independently in #416 and merged first; this PR is verified against that updated main branch.

Validation

• GitHub frontend checks: both passed on final head 6f18ee9.
• GitHub backend architecture gate: passed on final head 6f18ee9.
• Integrated yarn install --immutable, yarn check, and production Webpack + gulp build: passed. Zero lint/type errors; 5 existing production build warnings.
• Frontend tests: 9 retirement-focused tests and 4 chat-ui compatibility tests passed.
• Isolated backend build and architecture gate passed; backend source is identical after the frontend-only baseline merge.
• Focused Go suites: 481 test/subtest passes; one opt-in live-service E2E skipped by default.
• Retired API requests return 404 while the projects API remains available.
• Go/npm retired CLI commands exit 2 immediately without starting a service.
• Independent scope, data preservation, security, API, and frontend review: no findings.