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/result_item.html

@@ -4,7 +4,9 @@
     <a href="{{.URL}}" target="_blank" rel="noopener noreferrer">{{.SafeTitle}}</a>
   </div>
   <div class="result_url">
-    <img class="result-favicon" data-domain="{{.Domain}}" src="" alt="" loading="lazy" style="display:none">
+    {{if .Domain}}
+    <img class="result-favicon" src="/favicon/{{.Domain}}" alt="" loading="lazy" width="14" height="14">
+    {{end}}
     <a href="{{.URL}}" target="_blank" rel="noopener noreferrer">{{.URL}}</a>
     <span class="engine-badge" data-engine="{{.Engine}}">{{.Engine}}</span>
   </div>