Add state tracking and notifications DB support

Add kv_scan() for prefix-based key-value lookups (used by ClickUp task
state tracking). Add notifications table with add_notification() and
get_notifications_after() for the UI-agnostic notification bus.

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

cheddahbot/db.py

@@ -65,6 +65,12 @@ class Database:
                 key   TEXT PRIMARY KEY,
                 value TEXT NOT NULL
             );
+            CREATE TABLE IF NOT EXISTS notifications (
+                id          INTEGER PRIMARY KEY AUTOINCREMENT,
+                message     TEXT NOT NULL,
+                category    TEXT NOT NULL DEFAULT 'clickup',
+                created_at  TEXT NOT NULL
+            );
         """)
         self._conn.commit()
 
@@ -192,6 +198,32 @@ class Database:
         row = self._conn.execute("SELECT value FROM kv_store WHERE key = ?", (key,)).fetchone()
         return row["value"] if row else None
 
+    def kv_scan(self, prefix: str) -> list[tuple[str, str]]:
+        """Return all key-value pairs where key starts with prefix."""
+        rows = self._conn.execute(
+            "SELECT key, value FROM kv_store WHERE key LIKE ?", (prefix + "%",)
+        ).fetchall()
+        return [(r["key"], r["value"]) for r in rows]
+
+    # -- Notifications --
+
+    def add_notification(self, message: str, category: str = "clickup") -> int:
+        now = _now()
+        cur = self._conn.execute(
+            "INSERT INTO notifications (message, category, created_at) VALUES (?, ?, ?)",
+            (message, category, now),
+        )
+        self._conn.commit()
+        return cur.lastrowid
+
+    def get_notifications_after(self, after_id: int = 0, limit: int = 50) -> list[dict]:
+        """Get notifications with id > after_id."""
+        rows = self._conn.execute(
+            "SELECT id, message, category, created_at FROM notifications WHERE id > ? ORDER BY id ASC LIMIT ?",
+            (after_id, limit),
+        ).fetchall()
+        return [dict(r) for r in rows]
+
 
 def _now() -> str:
     return datetime.now(timezone.utc).isoformat()