fix: use single Preferences handler with method check instead of dead POST route

internal/httpapi/handlers.go

@@ -143,25 +143,19 @@ func (h *Handler) Autocompleter(w http.ResponseWriter, r *http.Request) {
 	_ = json.NewEncoder(w).Encode(suggestions)
 }
 
-// Preferences renders the preferences page.
+// Preferences handles GET and POST for the preferences page.
 func (h *Handler) Preferences(w http.ResponseWriter, r *http.Request) {
 	if r.URL.Path != "/preferences" {
 		http.NotFound(w, r)
 		return
 	}
+	if r.Method == "POST" {
+		// Preferences are stored in localStorage on the client via JavaScript.
+		// This handler exists only for form submission completeness.
+		http.Redirect(w, r, "/preferences", http.StatusFound)
+		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)
-}