fix: remove .next build artifacts from git tracking

- Add .next to .gitignore to prevent future conflicts
- Remove all build artifacts from git tracking
- Focus on source code changes only for cleaner merges

.next/server/middleware-manifest.json

@@ -1,6 +0,0 @@
-{
-  "version": 3,
-  "middleware": {},
-  "functions": {},
-  "sortedMiddleware": []
-}