fix: quick deploy duplicate detection, logout UX, backup toggle, CSP, SSE guard, and migration

- Detect existing projects with same image on quick deploy; show conflict dialog with options
- Move logout button to sidebar header as icon-only
- Replace backup checkbox with ToggleSwitch component
- Allow unsafe-inline in CSP script-src for SvelteKit hydration
- Guard SSE connection behind isAuthenticated() check
- Add notification_url ALTER TABLE migration for existing databases
- Restore RegisterPersistentLogger on event bus

internal/api/deploys.go

@@ -101,6 +101,7 @@ type quickDeployRequest struct {
 	Tag      string `json:"tag"`
 	Registry string `json:"registry"`
 	Port     int    `json:"port"`
+	Force    bool   `json:"force"` // skip duplicate check
 }
 
 // quickDeploy handles POST /api/deploy/quick.
@@ -124,6 +125,23 @@ func (s *Server) quickDeploy(w http.ResponseWriter, r *http.Request) {
 		req.Name = parts[len(parts)-1]
 	}
 
+	// Check for existing projects with the same image.
+	if !req.Force {
+		existing, err := s.store.GetProjectsByImage(req.Image)
+		if err != nil {
+			slog.Error("failed to check existing projects", "error", err)
+			respondError(w, http.StatusInternalServerError, "internal server error")
+			return
+		}
+		if len(existing) > 0 {
+			respondJSON(w, http.StatusConflict, map[string]any{
+				"message":           "A project with this image already exists",
+				"existing_projects": existing,
+			})
+			return
+		}
+	}
+
 	// Create project.
 	project, err := s.store.CreateProject(store.Project{
 		Name:     req.Name,