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/FeedbackToast.tsx

@@ -0,0 +1,65 @@
+import { HStack, VStack } from "@yaakapp-internal/ui";
+import { useState } from "react";
+import type { FeedbackFeature } from "../lib/featureFeedback";
+import { FEEDBACK_FEATURES } from "../lib/featureFeedback";
+import { invokeCmd } from "../lib/tauri";
+import { hideToastById, showToast } from "../lib/toast";
+import { Button } from "./core/Button";
+import { Input } from "./core/Input";
+
+interface Props {
+  feature: FeedbackFeature;
+}
+
+export function FeedbackToast({ feature }: Props) {
+  const [text, setText] = useState<string>("");
+
+  const handleDismiss = () => {
+    hideToastById(`feature-feedback-${feature}`);
+  };
+
+  const handleSend = () => {
+    // Fire-and-forget; failures are intentionally ignored
+    invokeCmd("cmd_send_feedback", { feature, text: text.trim() }).catch(() => {});
+    showToast({
+      id: `feature-feedback-${feature}`,
+      timeout: 3000,
+      color: "success",
+      message: "Thanks for the feedback!",
+    });
+  };
+
+  return (
+    <VStack space={2}>
+      <p className="text-sm font-semibold">{FEEDBACK_FEATURES[feature]}</p>
+      <div className="h-20">
+        <Input
+          size="xs"
+          // The editor forces its mono font on the scroller, so the override
+          // has to target it directly
+          className="[&_.cm-scroller]:font-sans! [&_.cm-scroller]:text-sm!"
+          label="Feedback"
+          hideLabel
+          stateKey={null}
+          multiLine
+          fullHeight
+          placeholder="Your thoughts..."
+          onChange={setText}
+        />
+      </div>
+      <HStack space={1.5} justifyContent="end">
+        <Button size="xs" color="secondary" variant="border" onClick={handleDismiss}>
+          Dismiss
+        </Button>
+        <Button
+          size="xs"
+          color="primary"
+          disabled={text.trim().length === 0}
+          onClick={handleSend}
+        >
+          Send
+        </Button>
+      </HStack>
+    </VStack>
+  );
+}