Add attention inbox and AI usage observability

src/database/client.ts

@@ -251,6 +251,27 @@ export function runMigrations(db: Database.Database): void {
       CREATE INDEX idx_conversation_automation_claims_status
         ON conversation_automation_claims(account_id, status, claimed_at);
     `),
+    () => db.exec(`
+      CREATE TABLE IF NOT EXISTS ai_usage (
+        id INTEGER PRIMARY KEY AUTOINCREMENT,
+        account_id TEXT,
+        operation TEXT NOT NULL,
+        requested_model TEXT NOT NULL,
+        actual_model TEXT,
+        outcome TEXT NOT NULL CHECK(outcome IN ('success', 'refusal', 'empty', 'error')),
+        prompt_tokens INTEGER NOT NULL DEFAULT 0,
+        completion_tokens INTEGER NOT NULL DEFAULT 0,
+        total_tokens INTEGER NOT NULL DEFAULT 0,
+        cost_usd REAL,
+        latency_ms INTEGER NOT NULL,
+        error TEXT,
+        created_at INTEGER NOT NULL,
+        FOREIGN KEY (account_id) REFERENCES reddit_accounts(account_id) ON DELETE SET NULL
+      );
+      CREATE INDEX IF NOT EXISTS idx_ai_usage_created_at ON ai_usage(created_at DESC);
+      CREATE INDEX IF NOT EXISTS idx_ai_usage_model ON ai_usage(actual_model, requested_model, created_at DESC);
+      CREATE INDEX IF NOT EXISTS idx_ai_usage_account ON ai_usage(account_id, created_at DESC);
+    `),
   ];
 
   let currentVersion = db.pragma('user_version', { simple: true }) as number;