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/components/git/GitCommitDialog.tsx

@@ -12,6 +12,7 @@ import { Banner, HStack, Icon, InlineCode, SplitLayout } from "@yaakapp-internal
 import classNames from "classnames";
 import { useCallback, useMemo, useState } from "react";
 import { modelToYaml } from "../../lib/diffYaml";
+import { trackFeatureUsage } from "../../lib/featureFeedback";
 import { resolvedModelName } from "../../lib/resolvedModelName";
 import { showConfirm } from "../../lib/confirm";
 import { showErrorToast } from "../../lib/toast";
@@ -55,6 +56,7 @@ export function GitCommitDialog({ syncDir, onDone, workspace }: Props) {
     setCommitError(null);
     try {
       await commit.mutateAsync({ message });
+      trackFeatureUsage("git-sync");
       onDone();
     } catch (err) {
       setCommitError(String(err));
@@ -66,6 +68,7 @@ export function GitCommitDialog({ syncDir, onDone, workspace }: Props) {
     try {
       const r = await commitAndPush.mutateAsync({ message });
       handlePushResult(r);
+      trackFeatureUsage("git-sync");
       onDone();
     } catch (err) {
       showErrorToast({