feat: add GET and POST /preferences route

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

cmd/kafka/main.go

@@ -84,6 +84,8 @@ func main() {
 	mux.HandleFunc("/healthz", h.Healthz)
 	mux.HandleFunc("/search", h.Search)
 	mux.HandleFunc("/autocompleter", h.Autocompleter)
+	mux.HandleFunc("/preferences", h.Preferences)
+	mux.HandleFunc("POST /preferences", h.PreferencesPOST)
 	mux.HandleFunc("/opensearch.xml", h.OpenSearch(cfg.Server.BaseURL))
 
 	// Serve embedded static files (CSS, JS, images).

internal/httpapi/handlers.go

@@ -142,3 +142,26 @@ func (h *Handler) Autocompleter(w http.ResponseWriter, r *http.Request) {
 	w.Header().Set("Content-Type", "application/json; charset=utf-8")
 	_ = json.NewEncoder(w).Encode(suggestions)
 }
+
+// Preferences renders the preferences page.
+func (h *Handler) Preferences(w http.ResponseWriter, r *http.Request) {
+	if r.URL.Path != "/preferences" {
+		http.NotFound(w, r)
+		return
+	}
+	if err := views.RenderPreferences(w, h.sourceURL); err != nil {
+		http.Error(w, err.Error(), http.StatusInternalServerError)
+	}
+}
+
+// PreferencesPOST handles form submission from the preferences page.
+// NOTE: This is a no-op. All preferences are stored in localStorage on the client
+// via JavaScript. This handler exists only for form submission completeness (e.g.,
+// if a form POSTs without JS). The JavaScript in settings.js handles all saves.
+func (h *Handler) PreferencesPOST(w http.ResponseWriter, r *http.Request) {
+	if r.URL.Path != "/preferences" {
+		http.NotFound(w, r)
+		return
+	}
+	http.Redirect(w, r, "/preferences", http.StatusFound)
+}