chore: add FVM config and update lockfile

- Add .fvmrc pinning Flutter 3.41.4
- Add .fvm/ to .gitignore
- Update pubspec.lock with latest transitive dependency versions

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

client/.gitignore

@@ -43,3 +43,6 @@ app.*.map.json
 /android/app/debug
 /android/app/profile
 /android/app/release
+
+# FVM Version Cache
+.fvm/