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/Pages/Blog/Post.cshtml

@@ -71,6 +71,7 @@
       .article-content strong{color:var(--dark);font-weight:600}
       .article-content a{color:var(--gold);border-bottom:1px solid var(--gold-pale)}
       .article-content blockquote{border-right:4px solid var(--gold);padding:.8rem 1.2rem;background:var(--gold-pale);border-radius:0 8px 8px 0;margin:1.2rem 0;font-style:italic;color:var(--mid)}
+      .article-content img{max-width:100%;height:auto;border-radius:12px;margin:1.2rem 0;display:block}
       /* ─── Tags ─────────────────────────────────────────────────────── */
       .article-tags{margin-top:2rem;padding-top:1.5rem;border-top:1px solid var(--border);display:flex;gap:.5rem;flex-wrap:wrap}
       .tag{background:var(--bg);border:1px solid var(--border);padding:.25rem .75rem;border-radius:50px;font-size:.78rem;color:var(--mid)}