feat(ui): add navigation trails to GitHub and work-item details

[Harry19081]

Problem

GitHub Issue, Work Item, Team Inbox assigned-item, and Pull Request details do not provide the persistent timeline navigation available in Sessions. Long descriptions and activity streams require manual scrolling, and earlier overlay-style navigation could disappear because of overflow, breakpoint, or marker-count gates.

Solution

Add a shared ScrollTrail that discovers semantic destinations, samples dense timelines to at most 20 markers, tracks the active destination, and supports click, hover, focus, and reduced-motion navigation. Work Item and Pull Request details now reserve a permanent 44px backgroundless and borderless right rail. GitHub Issues inherit the Work Item rail; Team Inbox assigned items and Pull Requests reuse the same owning detail surfaces. Sparse surfaces retain a root marker so the rail remains visible without overflow or multiple destinations.

The scroll listener is passive and frame-coalesced. Mutation and resize observation is scoped to the mounted detail content and fully disposed on unmount. No API, persistence, wire-format, dependency, or lockfile changes are included.

Potential risks

• The permanent rail reduces the detail content width by 44px; narrow and theme-specific visual behavior still needs manual desktop validation.
• Dense dynamic timelines can trigger scoped marker refreshes, though retained markers are capped at 20 and scroll work is coalesced to one animation frame.
• Pull Request Conversation has semantic destinations; Commits, Checks, and Changes intentionally retain the always-visible root fallback marker.
• No data migration or compatibility risk is introduced. Rollback is reverting the feature commit; merge commits only synchronize the latest develop behavior.

Verification

Passed before publication:

• pnpm exec vitest run src/modules/shared/layouts/blocks/ScrollTrail.test.ts src/modules/shared/components/ActivityTimeline/ActivityTimeline.test.ts src/modules/ProjectManager/WorkItems/components/GitHubIssueThreadSurface.test.ts src/modules/ProjectManager/WorkItems/components/WorkItemContent/__tests__/HistoryTab.test.ts src/modules/ProjectManager/WorkItems/components/WorkItemContent/__tests__/WorkItemDescriptionEditing.test.ts src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrDetailPanel.test.ts src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrConversationTab.test.ts — 50 tests across 7 files.
• pnpm exec eslint on all changed TypeScript and TSX files.
• pnpm exec prettier --check on all changed source and acceptance-test files.
• pnpm typecheck.
• pnpm check:circular — no circular dependencies across 6,188 modules.
• git diff --check origin/develop...HEAD.
• Repository pre-commit hook: lint-staged and staged TypeScript check.

Passed after merging current develop and resolving the shared PR-panel conflict:

• npx vitest run src/modules/shared/layouts/blocks/ScrollTrail.test.ts src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrDetailPanel.test.ts src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrConversationTab.test.ts src/modules/ProjectManager/WorkItems/components/GitHubIssueThreadSurface.test.ts src/modules/ProjectManager/WorkItems/components/WorkItemContent/__tests__/WorkItemDescriptionEditing.test.ts src/modules/shared/components/ActivityTimeline/ActivityTimeline.test.ts — 44 tests across 6 files.
• npx tsc --noEmit --pretty false.
• npx eslint src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrDetailPanel.tsx src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrDetailPanel.test.ts src/modules/WorkStation/CodeEditor/Panels/EditorPrimarySidebar/content/PullRequestContent/detail/PrConversationTab.tsx.
• Repository pre-commit hook: lint-staged, TypeScript, and scoped Rust clippy for integrations and orgtrack_core.
• GitHub reports the updated head as mergeable; CI is queued on the conflict-resolution commit.

Not run:

• Desktop visual QA and screenshots. Local UI control was not authorized, so manual validation of light/dark themes, narrow widths, loading states, and marker interaction remains pending.

Audit

The configured frontend-ui-audit skill was unavailable in this workspace. Manual review confirmed the rail reuses existing Session marker sizing, colors, focus treatment, sampling limit, reduced-motion behavior, and observer cleanup discipline.