build: add reproducible Android release verification

Pin Gradle inputs and dependency metadata, then enforce analyze, lint, build, R8, immutability, and regression gates in CI.

analysis_options.yaml

@@ -2,6 +2,8 @@ include: package:flutter_lints/flutter.yaml
 
 analyzer:
   exclude:
+    - build/**
+    - android/**
     - local_packages/**
     - whatsthis/**