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/Gallery.cshtml.cs

@@ -0,0 +1,36 @@
+using Microsoft.AspNetCore.Mvc.RazorPages;
+using Microsoft.EntityFrameworkCore;
+using DrSousan.Api.Data;
+using DrSousan.Api.Models;
+
+namespace DrSousan.Api.Pages;
+
+public class GalleryModel : PageModel
+{
+    private readonly AppDbContext _db;
+
+    public GalleryModel(AppDbContext db) => _db = db;
+
+    public List<GalleryItem> Items      { get; private set; } = new();
+    public List<string>      Categories { get; private set; } = new();
+
+    public async Task OnGetAsync()
+    {
+        Items = await _db.GalleryItems
+            .Where(g => g.IsActive)
+            .OrderBy(g => g.Order)
+            .ToListAsync();
+
+        Categories = Items
+            .Where(i => !string.IsNullOrWhiteSpace(i.Category))
+            .Select(i => i.Category.Trim())
+            .Distinct()
+            .ToList();
+
+        var siteName = (await _db.SiteSettings
+            .FirstOrDefaultAsync(x => x.Section == "hero" && x.Key == "name"))?.Value
+            ?? "دکتر سوسن آل‌طه";
+        ViewData["SiteName"] = siteName;
+        ViewData["Title"]    = $"گالری نتایج قبل و بعد | {siteName}";
+    }
+}