Add issue templates, CI workflows, and decentralization plan

- Add Gitea issue templates for bug reports and feature requests with
  structured YAML forms for version, database backend, and log level
- Add GitHub Actions CI workflow for automated testing on push/PR
- Add GitHub Actions release workflow for building multi-platform
  binaries on tag push with SHA256 checksums
- Add CONTRIBUTING.md with development setup, PR guidelines, and
  commit message format documentation
- Add DECENTRALIZE_NOSTR.md expansion plan outlining WireGuard tunnel,
  GUI installer, system tray, and proxy server architecture
- Update allowed commands in Claude settings
- Bump version to v0.35.5

Files modified:
- .gitea/issue_template/: Bug report, feature request, and config YAML
- .github/workflows/: CI and release automation workflows
- CONTRIBUTING.md: New contributor guide
- docs/plans/DECENTRALIZE_NOSTR.md: Expansion architecture plan
- .claude/settings.local.json: Updated allowed commands
- pkg/version/version: Version bump to v0.35.5

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

pkg/version/version

@@ -1 +1 @@
-v0.35.4
+v0.35.5