fix(git-diff): refresh diff data on screen mount and ignore agents.json

- Always request fresh git diff when screen opens (no caching)
- Add packages/server/agents.json to .gitignore (runtime data)
- Remove agents.json from git tracking

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

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

.gitignore

@@ -43,3 +43,6 @@ coverage/
 # Misc
 *.pem
 .vercel
+
+# Runtime agent data
+packages/server/agents.json