feat(auth): wire up refresh token endpoint and auto-refresh

- Add POST /api/refresh-token endpoint to router
- Auth store now calls refreshTokenIfNeeded on init and every hour
- Token refreshes automatically when within 2 weeks of expiry

backend/main.go

@@ -99,6 +99,8 @@ func main() {
 		r.Group(func(r chi.Router) {
 			r.Use(mw.RequireAuth)
 
+			r.Post("/refresh-token", authHandlers.RefreshTokenHandler)
+
 			r.Get("/user/profile", user.GetProfileHandler)
 			r.Put("/user/profile", user.UpdateProfileHandler)
 			r.Delete("/user/account", user.DeleteAccountHandler)