feat(gallery+editor): dedicated /gallery page, homepage teaser, in-content images

Homepage gallery:
- Show only 3 before/after samples as a teaser (was: all items)
- Add "مشاهده گالری کامل (N نمونه)" CTA when more than 3 exist
- Remove the now-pointless category tabs from the teaser

New /gallery page:
- Full before/after grid with category filter tabs (deduped from data)
- Responsive cards with قبل/بعد labels + captions, empty state
- Added to sitemap.xml (priority 0.8)

Blog content editor:
- New 🖼 تصویر toolbar button inserts an uploaded image at the cursor
  (direct upload, no forced crop) — for richer post bodies
- Responsive img styling on the public post page

Note: the filler-lab-soorat cover not showing is a data issue — that
post has an empty featuredImage in the DB (verified); re-upload + save
fixes it. The upload/save path itself is correct.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

DrSousan.Api/Program.cs

@@ -803,6 +803,7 @@ app.MapGet("/sitemap.xml", async (AppDbContext db, HttpContext ctx) =>
     }
 
     Url(baseUrl + "/", "1.0", "weekly", DateTime.UtcNow);
+    Url(baseUrl + "/gallery", "0.8", "weekly", DateTime.UtcNow);
     Url(baseUrl + "/blog", "0.9", "daily", DateTime.UtcNow);
     foreach (var p in published)
         Url($"{baseUrl}/blog/{p.Slug}", "0.8", "monthly", p.UpdatedAt);