QA fixes: real listing creation, profile save, favorites, missing pages

- SellItemPage: real file upload + API listing creation + activate
- CreateProfilePage: save profile via PUT /users/profile
- ProductDetailPage: wire edit/delete/message buttons, show edit for owner
- ListingCard: persist favorites via API, show real images
- Footer: connect newsletter subscribe to API
- Router: add /dashboard/listings and /dashboard/saved routes
- Backend: add GET /listings/favorites endpoint
- New pages: MyListingsPage, SavedItemsPage
- Fix unused imports causing build failures

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

package-lock.json

@@ -2952,7 +2952,6 @@
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-      "devOptional": true,
       "license": "BSD-2-Clause",
       "engines": {
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@@ -6443,6 +6442,7 @@
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         "cookie-parser": "^1.4.7",
         "cors": "^2.8.5",
+        "dotenv": "^16.4.0",
         "express": "^4.21.0",
         "express-rate-limit": "^7.5.0",
         "helmet": "^8.0.0",