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/config/config.go

@@ -160,12 +160,12 @@ func validateConfig(cfg *Config) error {
 func defaultConfig() *Config {
 	return &Config{
 		Server: ServerConfig{
-			Port:        8080,
+			Port:        5355,
 			HTTPTimeout: "10s",
 		},
 		Upstream: UpstreamConfig{},
 		Engines: EnginesConfig{
-			LocalPorted: []string{"wikipedia", "arxiv", "crossref", "braveapi", "qwant", "duckduckgo", "github", "reddit", "bing", "google", "youtube"},
+			LocalPorted: []string{"wikipedia", "arxiv", "crossref", "braveapi", "qwant", "duckduckgo", "github", "reddit", "bing", "google", "youtube", "bing_images", "ddg_images", "qwant_images"},
 			Qwant: QwantConfig{
 				Category:       "web-lite",
 				ResultsPerPage: 10,