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

backend/internal/api/router.go

@@ -14,10 +14,12 @@ type Handler struct {
 	steamcmd      *services.SteamCmdManager
 	scheduler     *services.Scheduler
 	streamer      *services.LogStreamer
+	dataDir       string
 	serverfileDir string
 	modsDir       string
 	cfgDir        string
 	profilesDir   string
+	frontendDir   string
 }
 
 func New(
@@ -28,7 +30,7 @@ func New(
 	steamcmd *services.SteamCmdManager,
 	scheduler *services.Scheduler,
 	streamer *services.LogStreamer,
-	serverfileDir, modsDir, cfgDir, profilesDir string,
+	dataDir, serverfileDir, modsDir, cfgDir, profilesDir, frontendDir string,
 ) *Handler {
 	return &Handler{
 		settings:      settings,
@@ -38,10 +40,12 @@ func New(
 		steamcmd:      steamcmd,
 		scheduler:     scheduler,
 		streamer:      streamer,
+		dataDir:       dataDir,
 		serverfileDir: serverfileDir,
 		modsDir:       modsDir,
 		cfgDir:        cfgDir,
 		profilesDir:   profilesDir,
+		frontendDir:   frontendDir,
 	}
 }
 
@@ -59,6 +63,7 @@ func (h *Handler) SetupRoutes(r *gin.Engine) {
 		api.POST("/server/steamcmd/download-mod", h.SteamCMDDownloadMod)
 		api.GET("/server/steamcmd/status", h.SteamCMDStatus)
 		api.GET("/server/paths", h.ServerPaths)
+		api.GET("/server/health", h.Health)
 
 		api.GET("/server/logs", h.ListLogs)
 		api.GET("/server/logs/:file", h.GetLog)