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>

src/db/schema.ts

@@ -58,6 +58,7 @@ export const threadCandidates = sqliteTable("thread_candidates", {
 	notes: text("notes"),
 	productUrl: text("product_url"),
 	imageFilename: text("image_filename"),
+	status: text("status").notNull().default("researching"),
 	createdAt: integer("created_at", { mode: "timestamp" })
 		.notNull()
 		.$defaultFn(() => new Date()),