Add server health endpoint and status page

Backend:
- New /api/server/health endpoint returning server, paths, disk,
  mods, steamcmd, and frontend status
- Health endpoint checks directory existence/writability, disk usage,
  server binary, and frontend dist availability

Frontend:
- New Status page (route /status) with sections for Server, SteamCMD,
  Mods, Frontend, Directories (with exists/writable badges), and
  Disk Usage (with size formatting and used-percent coloring)
- Paths are clickable to copy and use start-truncation (ellipsis on
  the left) with native hover tooltip
- Health API client integration with 10s auto-refresh

Misc:
- Update .gitignore and Makefile, minor Layout nav addition

.gitignore

@@ -8,6 +8,7 @@ backend/arma3-web-server
 
 data/
 serverfiles/
+dev-deploy/
 
 .env
 .DS_Store