fix: SPA routing and prompts table handling

- Add clean URL routing: /dashboard -> dashboard.html, /settings -> settings.html
- Add EnsurePromptsTable for dev environments where prompts table may not exist
- Fix nav links to use clean URLs instead of .html paths

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

main.go

@@ -38,12 +38,28 @@ func main() {
 	// Initialize handlers
 	handlers.Init(cfg)
 
+	// Ensure prompts table exists for dev environments
+	db.EnsurePromptsTable()
+
 	// Setup routes
 	mux := http.NewServeMux()
 
-	// Static files (frontend)
-	fs := http.FileServer(http.Dir("frontend"))
-	mux.Handle("/", fs)
+	// Static files with SPA-style routing for HTML pages
+	mux.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
+		path := r.URL.Path
+		// Map clean URLs to .html files
+		switch path {
+		case "/dashboard":
+			http.ServeFile(w, r, "frontend/dashboard.html")
+			return
+		case "/settings":
+			http.ServeFile(w, r, "frontend/settings.html")
+			return
+		}
+		// Default file server
+		fs := http.FileServer(http.Dir("frontend"))
+		fs.ServeHTTP(w, r)
+	})
 
 	// Auth routes (no auth required)
 	mux.HandleFunc("POST /api/auth/login", handlers.Login)