feat: add database schema, migrations, and API endpoints for span annotations

- Add span_label_types and span_annotations tables to schema
- Seed default span label types (bull_flag, bear_flag, etc.)
- Implement CRUD API endpoints for span label types
- Implement CRUD API endpoints for span annotations
- Add time swap validation in POST endpoint (start_time <= end_time)

drizzle/meta/_journal.json

@@ -22,6 +22,13 @@
       "when": 1770937855462,
       "tag": "0002_careful_synch",
       "breakpoints": true
+    },
+    {
+      "idx": 3,
+      "version": "6",
+      "when": 1771044740273,
+      "tag": "0003_demonic_captain_flint",
+      "breakpoints": true
     }
   ]
 }