feat(ui): dark theme redesign, fix image search and defaults

- Inline CSS in base.html (Inter, dark mode, sticky search, tabs, results)
- Remove HTMX/JS from templates; pagination via GET links
- Atmospheric side gradients + grid; wider column on large viewports
- Parse ?category= for HTML tabs (fixes Images category routing)
- Include bing_images, ddg_images, qwant_images in local_ported defaults
- Default listen port 5355; update Docker, compose, flake, README
- Favicon img uses /favicon/ proxy; preferences without inline JS

Made-with: Cursor

internal/views/templates/image_item.html

@@ -2,9 +2,9 @@
 <a class="image-result" href="{{.URL}}" target="_blank" rel="noopener noreferrer">
   <div class="image-thumb">
     {{if .Thumbnail}}
-    <img src="{{.Thumbnail}}" alt="{{.Title}}" loading="lazy" onerror="this.parentElement.classList.add('image-error')">
+    <img src="{{.Thumbnail}}" alt="{{.Title}}" loading="lazy">
     {{else}}
-    <div class="image-placeholder">🖼️</div>
+    <div class="image-placeholder" aria-hidden="true">🖼️</div>
     {{end}}
   </div>
   <div class="image-meta">