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/RecentHttpResponsesDropdown.tsx

@@ -10,6 +10,7 @@ import {
 } from "date-fns";
 import { useDeleteHttpResponses } from "../hooks/useDeleteHttpResponses";
 import { useKeyValue } from "../hooks/useKeyValue";
+import { trackFeatureUsage } from "../lib/featureFeedback";
 import { DismissibleBanner } from "./core/DismissibleBanner";
 import { Dropdown, type DropdownItem } from "./core/Dropdown";
 import { formatMillis } from "./core/HttpResponseDurationTag";
@@ -92,7 +93,10 @@ export const RecentHttpResponsesDropdown = function ResponsePane({
         </HStack>
       ),
       leftSlot: activeResponse?.id === r.id ? <Icon icon="check" /> : <Icon icon="empty" />,
-      onSelect: () => onPinnedResponseId(r.id),
+      onSelect: () => {
+        if (r.id !== latestResponseId) trackFeatureUsage("response-history");
+        onPinnedResponseId(r.id);
+      },
     });
   }