refactor(components): extract 4 DraftTab hooks (Wave 5.7 Phase A part 1)

[saagpatel]

What

Extracts 4 of the 5 planned Phase A hooks from src/components/Draft/DraftTab.tsx into dedicated sibling hook files. DraftTab gains its first-ever direct unit tests via renderHook coverage on each extracted hook.

• `useDraftApproval` — approval-search sub-feature (7 state, 2 async handlers, auto-reset effect)
• `useDraftFirstResponse` — first-touch response generator (3 state, 3 handlers)
• `useDraftChecklist` — checklist generation/update/toggle (5 state, 4 handlers)
• `useDraftIntake` — case-intake state + preset application + analyze + note-audience sync (1 state, 4 handlers, `INTAKE_PRESETS` constant)

File size: 2573 → 2283 LOC (-290, ~11% reduction).

Why

DraftTab.tsx is the largest file in the codebase (29 useState + 55 useCallback + forwardRef). The Wave 5 plan targets it as the final decomposition pass. Each hook encapsulates one distinct workflow concern (approval search, first response, checklist, intake) that is independent of the others and now testable in isolation.

How

Sequential hook extractions, one commit per hook. Each extraction:

1. Creates useDraft<Name>.ts in src/components/Draft/.
2. Moves the relevant state + callbacks out of the shell.
3. Exposes individual setters where useWorkspaceDraftState needs to hydrate fields on draft load (preserves that hook's API).
4. Adds a useDraft<Name>.test.ts with 2-3 renderHook tests.
5. Updates the shell to consume the hook return value.

Deferred to a follow-up PR

• useDraftGeneration hook (Phase A build(deps): bump numpy from 2.2.6 to 2.4.3 in /search-api #5) — the generation/alternatives pathway cross-touches 8+ pieces of shell state (response, sources, metrics, confidence, grounding, originalResponse, isResponseEdited, alternatives, alternativeIndex, generatingAlternative) that are read across dozens of downstream handlers. Extracting it cleanly requires careful setter plumbing that didn't fit this PR's commit budget.
• Phase B (sub-component panels) — DraftIntakePanel, DraftResponsePanel, DraftChecklistPanel.
• Phase C (shell reduction to ≤ 700 LOC) — depends on Phase B.
• Phase D (DraftTab integration tests) — depends on Phase C.

The 4 hook extractions here are independent and commit-revertable. The follow-up PR builds on the current shell.

Testing

• pnpm tsc --noEmit — clean.
• pnpm test — 196 tests pass (was 184; +12 new hook tests across 4 files).
• pnpm ui:gate:static — clean (only pre-existing warnings).
• Manual walk-through of the draft workflow should still render intake → first response → checklist → approval search → copy / save cleanly.

Risk / Notes

• DraftTab default export unchanged. DraftTabHandle interface unchanged.
• useWorkspaceDraftState consumer contract preserved — individual setters (setApprovalQuery, setApprovalSummary, setApprovalSources, setApprovalResults, setApprovalError, setCaseIntake, setFirstResponse, setChecklistItems, setChecklistCompleted, setChecklistError) are still exposed from the hooks and passed into the draft state manager.
• Each commit individually revertable.