test(02-01): add failing tests for thread service

- Add threads and threadCandidates tables to Drizzle schema
- Add Zod schemas for thread/candidate/resolve validation
- Add Thread/ThreadCandidate types to shared types
- Update test helper with threads and thread_candidates tables
- Write comprehensive failing tests for thread service

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

tests/helpers/db.ts

@@ -31,6 +31,33 @@ export function createTestDb() {
     )
   `);
 
+  sqlite.run(`
+    CREATE TABLE threads (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      name TEXT NOT NULL,
+      status TEXT NOT NULL DEFAULT 'active',
+      resolved_candidate_id INTEGER,
+      created_at INTEGER NOT NULL DEFAULT (unixepoch()),
+      updated_at INTEGER NOT NULL DEFAULT (unixepoch())
+    )
+  `);
+
+  sqlite.run(`
+    CREATE TABLE thread_candidates (
+      id INTEGER PRIMARY KEY AUTOINCREMENT,
+      thread_id INTEGER NOT NULL REFERENCES threads(id) ON DELETE CASCADE,
+      name TEXT NOT NULL,
+      weight_grams REAL,
+      price_cents INTEGER,
+      category_id INTEGER NOT NULL REFERENCES categories(id),
+      notes TEXT,
+      product_url TEXT,
+      image_filename TEXT,
+      created_at INTEGER NOT NULL DEFAULT (unixepoch()),
+      updated_at INTEGER NOT NULL DEFAULT (unixepoch())
+    )
+  `);
+
   sqlite.run(`
     CREATE TABLE settings (
       key TEXT PRIMARY KEY,