fix: RegisterPublicRoute pour pages HTML modules + masquer installés dans store

- RouteEntry.Public bool : routes sans auth (pages HTML navigables par Swup)
- RegisterPublicRoute() ajouté à Registry interface + coreRegistry
- main.go : switch public/auth/admin pour les routes modules
- modules.html : masque les modules déjà installés dans le store

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/modules/loader.go

@@ -80,6 +80,7 @@ type RouteEntry struct {
 	Path         string
 	Handler      http.HandlerFunc
 	RequireAdmin bool
+	Public       bool // true = pas d'authentification requise (ex: pages HTML)
 }
 
 type migrationEntry struct {
@@ -118,7 +119,12 @@ func newCoreRegistry(sqlDB *sql.DB, pool *sshpool.Pool, enc *crypto.Encryptor) *
 }
 
 func (r *coreRegistry) RegisterRoute(method, path string, handler http.HandlerFunc, requireAdmin bool) {
-	r.routes = append(r.routes, RouteEntry{method, path, handler, requireAdmin})
+	r.routes = append(r.routes, RouteEntry{Method: method, Path: path, Handler: handler, RequireAdmin: requireAdmin})
+}
+
+// RegisterPublicRoute enregistre une route sans authentification (ex: page HTML d'un module).
+func (r *coreRegistry) RegisterPublicRoute(method, path string, handler http.HandlerFunc) {
+	r.routes = append(r.routes, RouteEntry{Method: method, Path: path, Handler: handler, Public: true})
 }
 
 func (r *coreRegistry) RegisterWSChannel(channel string, handler WSHandler) {