Add database tools and improve tmux copy mode

Database Tools:
- Add lazysql: LazyGit-style TUI database management tool
- Add sqlite3: Official SQLite CLI for scripting and automation
- Comprehensive usage documentation for both tools
- Support for MySQL, PostgreSQL, and SQLite databases

Tmux Improvements:
- Fix copy mode to not exit after copying (copy-pipe vs copy-pipe-and-cancel)
- Allows multiple text selections without re-entering copy mode
- Manual exit control with q/Escape/Ctrl+c

System Optimizations:
- Add trusted binary caches for faster Nix builds
- Include nix-community and devenv cachix for improved performance

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

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

modules/tmux.nix

@@ -70,7 +70,7 @@
       
       # Better copy mode
       bind-key -T copy-mode-vi v send-keys -X begin-selection
-      bind-key -T copy-mode-vi y send-keys -X copy-pipe-and-cancel "pbcopy"
+      bind-key -T copy-mode-vi y send-keys -X copy-pipe "pbcopy"
       bind-key -T copy-mode-vi r send-keys -X rectangle-toggle
       
       # New window with current path