chore(repo): pin Flutter to the melos min via .fvmrc

Adds .fvmrc with the same Flutter floor the workspace declares in
melos.yaml (>=3.27.4) so contributors running fvm pick up the
right SDK automatically.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: xsahil03x

.fvmrc

@@ -0,0 +1,3 @@
+{
+  "flutter": "3.27.4"
+}

.gitignore

@@ -132,6 +132,9 @@ gradle-wrapper.jar
 **/fastlane/screenshots
 **/fastlane/test_output
 
+# FVM Version Cache
+.fvm/
+
 # Exceptions to the above rules
 !/pubspec.lock
 !**/example/web/sql-wasm.js