[codex] Derive Android version code from run number

[jjoonleo]

Summary

• Derive Android versionName from pubspec.yaml in release workflows.
• Use github.run_number as the generated Android versionCode for Play upload and release verification builds.
• Reset pubspec.yaml to 1.0.0+1 and update Android release docs so future redeploys do not require PRs that only bump +2, +3, etc.

Why

Google Play requires a monotonically increasing Android versionCode, but checked-in Flutter build suffix bumps create noisy PRs. Using the workflow run number keeps CI uploads monotonic while leaving the public version name manually controlled in pubspec.yaml.

Validation

• Parsed .github/workflows/android-play-internal.yml, .github/workflows/android-release-verify.yml, and pubspec.yaml with Ruby YAML.
• Ran git diff --check.
• Verified the shell extraction resolves 1.0.0+1 to Android build name 1.0.0.

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