feat: Implement subscription management and article saving features

- Added subscriptionPlan and subscriptionExpiresAt fields to UserProfile model.
- Enhanced profile routes to handle subscription state updates and expiration logic.
- Introduced email and password validation during user registration.
- Implemented link stripping for processed articles in the articles route.
- Added save article functionality with appropriate UI feedback in the frontend.
- Updated AccountSettings and FeedContent components to reflect subscription state and saved articles.
- Improved error handling and local storage management for user preferences.

frontend-BriefAI/src/services/apiService.ts

@@ -9,6 +9,8 @@ export type ProfileResponse = {
     email?: string
     macroTopics?: string[]
     keywords?: string[]
+    subscriptionPlan?: 'free' | 'pro'
+    subscriptionExpiresAt?: string | null
   }
 }
 
@@ -47,6 +49,7 @@ export const updateProfile = async (data: {
   userId?: string
   macroTopics?: string[]
   keywords?: string[]
+  subscriptionState?: 'free' | 'pro'
 }) => {
   // Sync to backend
   const backendRes = await authFetch('/api/profile', {
@@ -57,7 +60,7 @@ export const updateProfile = async (data: {
 
   // Opt-in sync to n8n if url is present and userId is known
   const n8nUrl = import.meta.env.VITE_N8N_URL;
-  if (n8nUrl && data.userId && data.macroTopics) {
+  if (n8nUrl && data.userId) {
     try {
       await fetch(`${n8nUrl}/briefai/profile/update`, {
         method: 'POST',
@@ -66,6 +69,7 @@ export const updateProfile = async (data: {
           userId: data.userId,
           macroTopics: data.macroTopics,
           keywords: data.keywords,
+          subscriptionState: data.subscriptionState,
         })
       });
     } catch (e) {