chore: add idb dependency missed in Phase 4 offline-capture commit

lib/offline/db.ts has imported idb since c048878 but the dependency
was never committed to package.json.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01CPf5Rc8QPx6V8KLEEgfKEQ

package-lock.json

@@ -11,6 +11,7 @@
         "@anthropic-ai/sdk": "^0.111.0",
         "@supabase/ssr": "^0.12.0",
         "@supabase/supabase-js": "^2.110.2",
+        "idb": "^8.0.3",
         "next": "^15.5.20",
         "pdf-lib": "^1.17.1",
         "react": "^19.2.7",
@@ -5819,6 +5820,12 @@
         "node": ">=20.0.0"
       }
     },
+    "node_modules/idb": {
+      "version": "8.0.3",
+      "resolved": "https://registry.npmjs.org/idb/-/idb-8.0.3.tgz",
+      "integrity": "sha512-LtwtVyVYO5BqRvcsKuB2iUMnHwPVByPCXFXOpuU96IZPPoPN6xjOGxZQ74pgSVVLQWtUOYgyeL4GE98BY5D3wg==",
+      "license": "ISC"
+    },
     "node_modules/ignore": {
       "version": "5.3.2",
       "resolved": "https://registry.npmjs.org/ignore/-/ignore-5.3.2.tgz",