chore: fix all analyzer issues and upgrade dependencies
Resolved all 88 analyzer issues and modernized the codebase with dependency
updates and Android build configuration improvements.
## Code Quality Fixes (88 → 0 issues)
- Replace deprecated withOpacity() with withValues() for Color objects
- Add specific exception types to catch clauses (on Exception)
- Fix unawaited future in feed provider tests
- Add missing type annotation to OAuth service
- Fix line length violations (80 char limit)
- Fix control body formatting (multi-line statements)
- Convert positional bool params to named params in tests
- Apply automated dart fix suggestions
## Dependency Management
- Remove unused bluesky package and 18 transitive dependencies
- Remove all discontinued packages (at_identifier, at_uri, nsid)
- Upgrade flutter_lints: 5.0.0 → 6.0.0
- Upgrade 19 compatible transitive dependencies
- Update Flutter SDK: 3.29.2 → 3.35.7
- Update Dart SDK: 3.7.2 → 3.9.2
## Android Build Configuration
- Upgrade Kotlin: 1.8.22 → 2.1.0 (required by Flutter)
- Force Java 11 compatibility across all plugins
- Set Kotlin JVM target to 11 for consistency
- Eliminate all build warnings
Result: Clean analyzer, no build warnings, modern dependencies
🤖 Generated with [Claude Code](https://claude.com/claude-code)
Co-Authored-By: Claude <noreply@anthropic.com>