feat: add admin-toggleable auto-approve setting

- Extension settings table with auto_approve boolean
- GET/PUT /api/v1/settings endpoints (LNbits admin only)
- Settings card in admin UI with toggle
- When auto_approve is enabled, non-admin events skip approval

Closes aiolabs/events#11

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

migrations.py

@@ -214,3 +214,20 @@ async def m009_add_nostr_columns(db):
     await db.execute(
         "ALTER TABLE events.events ADD COLUMN nostr_event_created_at INTEGER;"
     )
+
+
+async def m010_add_events_settings(db):
+    """
+    Create extension settings table for admin-configurable options.
+    """
+    await db.execute(
+        """
+        CREATE TABLE IF NOT EXISTS events.settings (
+            id INTEGER PRIMARY KEY DEFAULT 1,
+            auto_approve BOOLEAN NOT NULL DEFAULT FALSE
+        );
+        """
+    )
+    await db.execute(
+        "INSERT OR IGNORE INTO events.settings (id, auto_approve) VALUES (1, FALSE);"
+    )