Add comprehensive TODO list and update metadata

- Create TODO.md with all remaining issues and planned features
- Update metadata.json with repository URL to fix warning
- Update author name to Keith Smith

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

metadata.json

@@ -4,5 +4,6 @@
     "description": "Advanced window tiling manager with customizable zone layouts",
     "version": "0.1.0",
     "cinnamon-version": ["5.0", "5.2", "5.4", "5.6", "6.0"],
-    "author": "Your Name"
+    "author": "Keith Smith",
+    "url": "https://git.firebugit.com/ksmith/GridSnap"
 }