refactor(list): extract DateHierarchyBar from ListPage into @dar/list (#428)

[MartinCastroAlvarez]

First incremental step of #428 (decompose the ListPage / DetailPage god-components). Starting with ListPage since it's the larger one and — unlike DetailPage — isn't touched by the in-flight #427/#465 drafts, so no collision.

Role: Author / Architect.

Change

Lift the self-contained date_hierarchy drill-down bar (and its MONTH_NAMES) out of ListPage.tsx into a props-driven, individually-testable component in @dar/list — the package #303 wants the list page to live in. ListPage now composes <DateHierarchyBar dh=… onNavigate=… />.

• No behaviour change (component logic copied verbatim; props identical).
• ListPage.tsx: 837 → 729 lines (−108).
• @dar/list gains react as a peer/dev dep (mirroring @dar/search) and is wired into apps/web.
• Adds the package's first vitest (year/month drill-down + breadcrumb-up).

This establishes the extraction+test pattern; follow-up PRs lift the filter/columns modals, pagination, and the list_editable controller (each its own small PR, per the issue).

Verification

• pnpm -r typecheck clean (13/13), pnpm lint clean (incl. eslint import-boundary on @dar/list + dark-mode guard), pnpm test 97 passed (16 files; +3 new).
• Backend untouched.
• (CI runs only CodeQL — see CI stability: the test suites don't run in CI — test regressions merge undetected (only CodeQL gates) #452.)

🤖 Generated with Claude Code

[martin-castro-laminr-ai]

Architect review + merge (multi-role, authorised on this repo).

Verified locally in a clean worktree off pr-501:

• pnpm -r typecheck — clean (13/13)
• pnpm lint — clean (eslint --max-warnings 0, stylelint, import-boundary + dark-mode coverage)
• pnpm test — 97 passed (16 files, +3 new)

The extraction is verbatim (component logic + MONTH_NAMES moved unchanged; props identical), ListPage.tsx shrinks by ~108 LOC, @dar/list gains its first vitest, and the import-boundary lint stays green. No backend touched. Clears the bar for #428/#303. Merging.