test(08-01): add failing tests for candidate status field

- 5 tests: create with/without status, update status, getThreadWithCandidates includes status
- Test helper updated with status column in thread_candidates CREATE TABLE

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

tests/helpers/db.ts

@@ -54,6 +54,7 @@ export function createTestDb() {
       notes TEXT,
       product_url TEXT,
       image_filename TEXT,
+      status TEXT NOT NULL DEFAULT 'researching',
       created_at INTEGER NOT NULL DEFAULT (unixepoch()),
       updated_at INTEGER NOT NULL DEFAULT (unixepoch())
     )