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>

flake.nix

@@ -21,6 +21,16 @@
         ];
 
       nix.settings.experimental-features = "nix-command flakes";
+      nix.settings.substituters = [
+        "https://cache.nixos.org/"
+        "https://nix-community.cachix.org"
+        "https://devenv.cachix.org"
+      ];
+      nix.settings.trusted-public-keys = [
+        "cache.nixos.org-1:6NCHdD59X431o0gWypbMrAURkbJ16ZPMQFGspcDShjY="
+        "nix-community.cachix.org-1:mB9FSh9qf2dCimDSUo8Zy7bkq5CX+/rkCWyvRCYg3Fs="
+        "devenv.cachix.org-1:w1cLUi8dv3hnoSPGAuibQv+f9TZLr6cv/Hm9XgU50cw="
+      ];
       system.stateVersion = 6;
       nixpkgs.hostPlatform = "aarch64-darwin";
 
@@ -48,6 +58,8 @@
         lftp
         termscp
         httpie
+        lazysql
+        sqlite
         claude-code.packages.aarch64-darwin.claude-code
         nerd-fonts.fira-code
         nerd-fonts.jetbrains-mono