Add in-app edit UI for dashboard config

A web editor at /edit for managing pages and widgets without hand-editing YAML:

- Page list and per-page widget views with breadcrumb navigation
- Add/delete pages, add/delete/reorder widgets within a column
- Per-widget textarea editor with curated starter templates, widget-specific
  help (example, full field reference, link to upstream docs), and inline
  error rendering that preserves the user's edits on validation failure
- Pre-save validation via newConfigFromYAML; atomic temp+rename writes with
  .bak backup; YAML edits go through yaml.Node so comments and unresolved
  ${env:X}/${secret:X} tokens survive round-trips
- Auth gate: editing requires auth.users to be configured, or
  admin.allow-without-auth: true as an explicit opt-in for trusted networks
- Pencil button on the dashboard near the theme picker for quick access
- Admin views read fresh from disk so the list updates immediately after
  saves rather than lagging the fsnotify watcher

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

internal/glance/glance.go

@@ -28,9 +28,10 @@ const STATIC_ASSETS_CACHE_DURATION = 24 * time.Hour
 var reservedPageSlugs = []string{"login", "logout"}
 
 type application struct {
-	Version   string
-	CreatedAt time.Time
-	Config    config
+	Version    string
+	CreatedAt  time.Time
+	Config     config
+	ConfigPath string
 
 	parsedManifest []byte
 
@@ -44,11 +45,12 @@ type application struct {
 	failedAuthAttempts     map[string]*failedAuthAttempt
 }
 
-func newApplication(c *config) (*application, error) {
+func newApplication(c *config, configPath string) (*application, error) {
 	app := &application{
 		Version:    buildVersion,
 		CreatedAt:  time.Now(),
 		Config:     *c,
+		ConfigPath: configPath,
 		slugToPage: make(map[string]*page),
 		widgetByID: make(map[uint64]widget),
 	}
@@ -450,6 +452,18 @@ func (a *application) server() (func() error, func() error) {
 		w.WriteHeader(http.StatusOK)
 	})
 
+	mux.HandleFunc("GET /edit", a.handleAdminIndex)
+	mux.HandleFunc("GET /edit/pages/{page}", a.handleAdminPage)
+	mux.HandleFunc("GET /edit/pages/{page}/widgets/{col}/{idx}", a.handleAdminWidget)
+
+	mux.HandleFunc("POST /edit/api/pages", a.handleAdminAddPage)
+	mux.HandleFunc("POST /edit/api/pages/{page}/delete", a.handleAdminDeletePage)
+	mux.HandleFunc("GET /edit/pages/{page}/widgets/{col}/new", a.handleAdminNewWidget)
+	mux.HandleFunc("POST /edit/api/pages/{page}/widgets/{col}/new", a.handleAdminCreateWidget)
+	mux.HandleFunc("POST /edit/api/pages/{page}/widgets/{col}/{idx}", a.handleAdminEditWidget)
+	mux.HandleFunc("POST /edit/api/pages/{page}/widgets/{col}/{idx}/delete", a.handleAdminDeleteWidget)
+	mux.HandleFunc("POST /edit/api/pages/{page}/widgets/{col}/{idx}/move", a.handleAdminMoveWidget)
+
 	if a.RequiresAuth {
 		mux.HandleFunc("GET /login", a.handleLoginPageRequest)
 		mux.HandleFunc("GET /logout", a.handleLogoutRequest)