chore: cleanup repository and update gitignore

- Removed binary 'gophergate'
- Removed 'data/llm_proxy.db' from source control (kept locally)
- Removed old database backups in 'data/backups/'
- Updated .gitignore to exclude data directory and gophergate binary

.gitignore

@@ -4,6 +4,8 @@
 /target
 /llm-proxy
 /llm-proxy-go
+/gophergate
+/data/
 *.db
 *.db-shm
 *.db-wal