feat(a11y): migrate accessibility core to DSH 0.1.7-rc.2

[mattheliu]

Summary

Merge official dsh-v0.1.7-rc.2 (477b4f420553e8a52c2fbccc464d7561b239c443) into the existing accessibility core. This PR deliberately targets the exact rc.2 baseline, not the fork's historical default branch. npm next=0.2.0-rc.1 is a separate investigation.

Companion integration: omdsh-dev/dsh-accessibility#29

• Preserve semantic landmarks, conversation records/live announcements, keyboard composites, modal focus restoration, contextual labels, accessible separators, and explicit low-noise headless presentation.
• Adapt changed upstream component and fixture APIs. Fix workspace tree focus/states, permission/model trigger focus, modal-layer behavior, and Fetch links nested inside disclosure buttons.
• Preserve upstream menu-check sizing and focus-ring treatments. Update reviewed ARIA expectations and exercise the changed keyboard behavior; do not blindly accept snapshots.

Local verification

• Full GUI: 590 files passed; 9,274 tests passed, 1 explicit skip.
• Core accessibility: 40 passed, Chromium/Firefox/WebKit; 2 forced-colors skips outside Chromium.
• External companion integration: 5 passed across the three browsers with clean core 1e53eedb532a7965aee4d4c294c2ee313cf15906 and companion 20b3b151858d9b9e6cb986501c00faf6960eb1b6.
• Core, companion, and live AT lab startup/cleanup smoke passed on those same clean revisions. These runs did not observe a screen reader or exercise human tasks.
• Build, 18 hygiene gates, 20 quick documentation gates, 42 full doc-sync gates, and headless expected output (17 tests) passed. CLI help/usage and keyless smoke passed.
• Full lint found one overlong declaration, cleared by a formatting-only wrap plus owning-file lint. Normal commit hooks and the normal pre-push incremental typecheck passed.
• General Web replay was covered in partitions. The remaining 144-file run initially had 21 failing files; each failed scope was repaired and rerun, including a final 3-file/12-test pass. This is not a claim that a single final full Web invocation was green.
• An earlier full GUI run timed out on Markdown registration; a later isolated full run passed without retry/timeout changes. Its earlier cause is not established.
• Steering/turn-tail Session recordings were not refreshed. The goal-action fixture owner refreshed only the current v4 header's startsSeries field and passed replay; older generations were untouched.
• Added-lines credential/private-key/local-home pattern scan found no matches. This is not a full security audit.

Review and release boundary

Keep this PR unmerged pending designer/product review of the user-perceivable interaction changes and remote CI. No npm publication or release tag is included. Automatic browser checks do not establish actual speech, OS accessibility-API mapping, or independent completion by disabled developers. Real VoiceOver/NVDA and disabled-user evidence remains pending; historical campaign records stay bound to their original revisions.