feat(08-01): add status column to threadCandidates and wire through backend

- Schema: status TEXT NOT NULL DEFAULT 'researching' on thread_candidates
- Zod: candidateStatusSchema enum (researching/ordered/arrived) added to createCandidateSchema
- Service: getThreadWithCandidates selects status, createCandidate sets status, updateCandidate accepts status
- Client hooks: CandidateWithCategory and CandidateResponse types include status field
- Migration generated and applied

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

drizzle/meta/_journal.json

@@ -1,20 +1,27 @@
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