feat: replace mock mode with real backend dev mode

Add --dev flag to `opal server start` that disables auth (injects
userID=1 for all requests) and exposes a /auth/dev-session endpoint,
so the frontend can develop against a real backend without OAuth
config. Remove VITE_MOCK_MODE and all mock data/branches from the
frontend stores. Add scripts/dev.sh to start both services locally.

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

opal-task/internal/api/server.go

@@ -11,15 +11,17 @@ import (
 
 // Server represents the API server
 type Server struct {
-	router chi.Router
-	addr   string
+	router  chi.Router
+	addr    string
+	devMode bool
 }
 
 // NewServer creates a new API server
-func NewServer(addr string) *Server {
+func NewServer(addr string, devMode bool) *Server {
 	s := &Server{
-		router: chi.NewRouter(),
-		addr:   addr,
+		router:  chi.NewRouter(),
+		addr:    addr,
+		devMode: devMode,
 	}
 	s.setupRoutes()
 	return s
@@ -39,16 +41,37 @@ func (s *Server) setupRoutes() {
 		JSON(w, http.StatusOK, map[string]string{"status": "ok"})
 	})
 
-	// OAuth endpoints (no auth required)
-	r.Get("/auth/login", handlers.GetLoginURL)
-	r.Get("/auth/callback", handlers.OAuthCallback)
-	r.Post("/auth/callback", handlers.OAuthCallback)
-	r.Post("/auth/refresh", handlers.RefreshToken)
-	r.Post("/auth/logout", handlers.Logout)
+	if s.devMode {
+		// Dev mode: fake session endpoint so the frontend can "log in"
+		r.Get("/auth/dev-session", func(w http.ResponseWriter, r *http.Request) {
+			JSON(w, http.StatusOK, map[string]interface{}{
+				"access_token":  "dev-token",
+				"refresh_token": "",
+				"expires_at":    9999999999,
+				"token_type":    "bearer",
+				"user": map[string]interface{}{
+					"id":       1,
+					"username": "dev",
+					"email":    "dev@localhost",
+				},
+			})
+		})
+	} else {
+		// OAuth endpoints (no auth required)
+		r.Get("/auth/login", handlers.GetLoginURL)
+		r.Get("/auth/callback", handlers.OAuthCallback)
+		r.Post("/auth/callback", handlers.OAuthCallback)
+		r.Post("/auth/refresh", handlers.RefreshToken)
+		r.Post("/auth/logout", handlers.Logout)
+	}
 
 	// Protected routes
 	r.Group(func(r chi.Router) {
-		r.Use(AuthMiddleware())
+		if s.devMode {
+			r.Use(DevAuthMiddleware())
+		} else {
+			r.Use(AuthMiddleware())
+		}
 
 		// Tasks
 		r.Route("/tasks", func(r chi.Router) {