Add in-app micro-feedback prompts for new features

Show a one-time toast asking how a feature is working after its third
successful use, with an optional comment sent anonymously to the Yaak
API (feature key, text, app version, and OS only — nothing identifying,
and nothing is sent unless the user clicks Send).

- New cmd_send_feedback Tauri command posts fire-and-forget via the
  shared API client (localhost in dev)
- Feature keys registry (cookie-editor, response-history, sse-summary,
  git-sync) with per-feature use counting in the key-value store
- "Never ask for feedback" setting to disable prompts entirely
- Toast gains dynamicHeight and hideDismiss props for richer content
- Fix missing vertical padding on xs/2xs multiline inputs
- Fix unused-import and dead-code warnings in yaak-system-appearance
  on non-Linux builds

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

apps/yaak-client/lib/toast.tsx

@@ -37,6 +37,11 @@ export function showToast({
   return id;
 }
 
+export function hideToastById(id: string) {
+  const toast = jotaiStore.get(toastsAtom).find((t) => t.id === id);
+  if (toast) hideToast(toast);
+}
+
 export function hideToast(toHide: ToastInstance) {
   jotaiStore.set(toastsAtom, (all) => {
     const t = all.find((t) => t.uniqueKey === toHide.uniqueKey);