fix: enforce note ownership across all API endpoints

- Add userId check to /api/notes/reorder (was completely unprotected)
- Scope syncNoteTags by userId to prevent cross-user tag pollution
- Verify attachmentId belongs to noteId in attachment operations (IDOR fix)
- Remove DEFAULT 0 from userId columns so missing userId fails loudly
- Update test helpers and test data to provide required userId

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

drizzle/meta/_journal.json

@@ -8,6 +8,13 @@
       "when": 1773000424830,
       "tag": "0000_wooden_vargas",
       "breakpoints": true
+    },
+    {
+      "idx": 1,
+      "version": "6",
+      "when": 1773016788899,
+      "tag": "0001_strange_lord_hawal",
+      "breakpoints": true
     }
   ]
 }