refactor(components): extract useWorkspaceArtifacts hook

[saagpatel]

What

Extracts the workspace-artifact concerns out of `DraftTab.tsx` into a new `useWorkspaceArtifacts` hook:

• similar-cases state (`similarCases`, `similarCasesLoading`, `compareCase`)
• debounced auto-refresh effect
• `handleRefreshSimilarCases`, `handleCompareLastResolution`, `handleCompareSimilarCase`
• `handleSaveCurrentResolutionKit`, `handleApplyResolutionKit`
• `handleToggleWorkspaceFavorite`

Shell reduction: 1738 → 1551 LOC (-187 on this PR).

Why

These callbacks form one cohesive concern (workspace artifacts — similar cases, resolution kits, favorites) and share the `similarCases`/`compareCase` state. Auto-refresh used to live in a useEffect in the shell that drove `handleRefreshSimilarCases`; it moves into the hook so the hook owns both state and the effect that populates it.

How

1. Create `useWorkspaceArtifacts.ts` with the state + 6 self-contained handlers.
2. Place the hook call between `useWorkspaceDerivedArtifacts` (provides `kbDraft`) and `useWorkspaceDraftState` (consumes `setCompareCase`). This ordering is load-bearing.
3. Keep `loadSimilarCaseIntoWorkspace` and `handleOpenSimilarCase` in the shell — they depend on `handleLoadDraft` from `useWorkspaceDraftState`, which is called AFTER the artifacts hook. Moving those would require either deferred refs or a third hook.
4. Replace `setSimilarCases([])/setSimilarCasesLoading(false)/setCompareCase(null)` in `handleClear` with a single `resetWorkspaceArtifacts()` call.
5. Drop now-unused imports: `applyResolutionKit`, `buildResolutionKitFromWorkspace`, `buildSimilarCases`, `ResolutionKit` type, `WorkspaceFavorite` type.
6. Add `useWorkspaceArtifacts.test.ts` (7 tests) covering: debounce auto-refresh fires, disabled-flag skip, empty-response compare guard, save kit + log + refresh, apply kit + focus-intake, favorite add, favorite remove.

Testing

• `pnpm tsc --noEmit` — clean.
• `pnpm test` — 227 pass (was 220; +7 new hook tests).
• `pnpm ui:gate:static` — exit 0.

Risk / Notes

• `DraftTabHandle` unchanged.
• Debounce delay and query-building logic for similar-cases preserved exactly.
• Resolution-kit payload shape unchanged.
• Favorite toggle save/delete branching unchanged.

Wave 5 status after this PR

• DraftTab: 2573 → 1551 LOC (-1022, ~40% total reduction)
• Tests: 184 → 227 (+43 direct Draft concern tests)
• 11 hooks + 1 panel extracted + 1 handle pin
• ~550 LOC from the 1000-target. Two more concerns (response actions + lifecycle effects) remain in the roadmap.