fix(ci): use 'stable' for Flutter version instead of non-existent 3.41.x

The Mac runner cannot resolve Flutter 3.41.x (does not exist). Switch
to 'stable' so the subosito/flutter-action always picks the latest
stable release regardless of runner architecture.

.gitea/workflows/ci.yml

@@ -16,7 +16,7 @@ concurrency:
   cancel-in-progress: true
 
 env:
-  FLUTTER_VERSION: "3.41.x"
+  FLUTTER_VERSION: "stable"
 
 jobs:
   # ── Stage 1: Lint & static analysis ──────────────────────────────

.gitea/workflows/release.yml

@@ -10,7 +10,7 @@ on:
       - "v*"
 
 env:
-  FLUTTER_VERSION: "3.41.x"
+  FLUTTER_VERSION: "stable"
 
 jobs:
   # ── Lint (gate) ─────────────────────────────────────────────