[codex] Offline-first app stabilization base

[berlogabob]

Summary

Base PR for the existing offline-first app stabilization groundwork that #49 builds on. This branch captures the pre-test-stabilization new-hope work up to commit 5cfd400, plus the toolchain/dependency update required for current stable CI.

It includes broader app, sync, local storage, test harness, generated documentation changes, and the Flutter/Dart dependency refresh that the focused test-suite stabilization depends on.

Toolchain And Dependencies

Updated to the current stable Flutter toolchain identified from Flutter release metadata:

• Flutter 3.44.0 stable
• Dart 3.12.0
• CI subosito/flutter-action Flutter version updated to 3.44.0
• pubspec.yaml SDK constraint updated to ^3.12.0
• dependencies upgraded to the latest stable compatible resolution

Note: package_info_plus and share_plus remain on their latest stable versions compatible with stable file_picker because the newest stable Plus packages require win32 ^6, while stable file_picker 11.0.2 still depends on win32 ^5. No prerelease package versions are present in pubspec.lock.

Stack

• Base PR: this PR (codex/offline-first-base -> main)
• Follow-up PR: [codex] Stabilize offline-first Flutter test suite #49 (codex/offline-first-stabilization -> codex/offline-first-base)

Validation

The rebased follow-up stabilization branch was validated with:

• /tmp/flutter-3.44.0/flutter/bin/flutter analyze
• /tmp/flutter-3.44.0/flutter/bin/flutter build apk --debug
• /tmp/flutter-3.44.0/flutter/bin/flutter test --reporter compact --concurrency=1 (907 tests passed)

This PR should be reviewed first because #49 depends on these base changes.