Flutter 3.47.5 is stable (pinned: 3.47.4)

[github-actions]

Flutter 3.47.5 (Dart 3.13.4) became stable on 2026-09-18.
This repo pins 3.47.4 (Dart 3.13.3) in .fvmrc.

Important

The Dart SDK also moves (3.13.3 -> 3.13.4), so the SDK-vendored
transitives in pubspec.lock (meta, matcher, test_api,
vector_math, intl) will change. The lock must be regenerated on
the new pin or CI fails at flutter pub get --enforce-lockfile.

Bump deliberately, in its own PR, with the fallout fixed in the same PR:

• Update .fvmrc to 3.47.5. That is the only place the version lives: both workflows read it via flutter-version-file, and the ARM64 leg reads it with jq.
• Install 3.47.5 locally, run flutter pub get (no --enforce-lockfile) to regenerate pubspec.lock, and commit it.
• dart format . and commit any reflowed files.
• flutter analyze and fix new lints.
• flutter test.

Not urgent: staying a release behind is fine. The point is that the move is a
commit, not a surprise.

_{Opened automatically by .github/workflows/flutter-stable-watch.yml.}