chore: harden repo for open source contributors

- Expand .gitignore with .env, .DS_Store, node_modules, editor files,
  and macOS iCloud duplicate patterns
- Add security section to CLI README warning against hardcoded keys
- Update AGENTS.md with CLI tools in repo structure and build commands
- Trash 40 macOS "2.md" duplicate files from working tree

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.gitignore

@@ -1,2 +1,25 @@
+# Dependencies
+node_modules/
+
+# Environment variables / secrets
+.env
+.env.*
+!.env.example
+
+# macOS
+.DS_Store
+**/. DS_Store
+
+# macOS / iCloud duplicate files
+* 2.*
+* 2/
+
 # Remotion video project
 video/
+
+# Editor
+*.swp
+*.swo
+*~
+.idea/
+.vscode/