Remove auto-generated projects.json from git tracking

- Add config/projects.json to .gitignore
- Remove from git tracking while preserving local file
- projects.json is auto-generated by Home Manager from projects.nix
- Prevents merge conflicts and version control noise from machine-specific paths

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

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

.gitignore

@@ -16,4 +16,7 @@ Thumbs.db
 .#*
 #*#
 *.swp
-*.swo
+*.swo
+
+# Auto-generated files
+config/projects.json