feat(offline): play downloaded video, and drain the offline sync queue (0.4.6)

Bundles this session's work plus the concurrent search/offline/player changes.
Every gate passes on the combined tree: 885 frontend tests, 610 Rust tests,
clippy clean, boundary clean, trace coverage 86%.

Offline video playback — four separate defects, each of which alone stopped it:

  DR-133  A completed download's file_path is already absolute (the worker
          rewrites it on completion), but the player rooted it a second time and
          handed the webview /data/user/0/app//data/user/0/app/videos/x.mp4.
  DR-134  The asset protocol was never enabled: no protocol-asset feature and no
          assetProtocol config, so convertFileSrc produced URLs nothing answered.
          Also silently defeated the cached-thumbnail path, which fails soft to
          the server copy and hid it whenever the server was reachable.
  DR-137  Tauri's asset protocol answers a range-less request by reading the
          whole file into memory, and only advertises Accept-Ranges from inside
          its range branch, so the first request never learns ranges exist.
          Chromium gave up with PIPELINE_ERROR_READ after ~31s. Local media is
          now served by a loopback HTTP server: bounded 4 MiB chunks streamed
          from the file handle, every response length-delimited, and a range-less
          request answered with one chunk rather than the file. Confined by a
          per-session token and to the app data directory, because loopback is
          shared between apps on Android.
  DR-138  Release builds set usesCleartextTraffic=false, so Android rejected the
          request to that server before any I/O. A network-security-config
          exempts 127.0.0.1 only; a remote server must still be HTTPS.

Downloads:

  DR-135  download_item never records media_type and the reconnect resolver read
          that NULL as 'audio', so a movie queued from a media card had its URL
          resolved by get_audio_stream_url and completed as an audio-only
          transcode. The item's own type now decides.
  DR-136  Rows already downloaded that way are requeued on reconnect, since
          prevention alone leaves them reading "downloaded" and still unplayable.

Known limitation: a download taken at `original` quality is a byte copy of the
source, so it can be any container. One such file is an AVI holding XVID, which
the webview cannot play in any case — the media server serves it correctly and
Chromium refuses it. That needs either a transcoded download preset or the
native ExoPlayer surface work, and is not addressed here.

Also fixes two ID collisions between concurrent work: DR-143 defined twice
(search vs offline gate) and UT-131 defined twice (Episode Focus hero vs channel
cap). The search requirement is now DR-147 and the channel-cap test UT-141, with
their code references and matrix rows updated.

src/lib/components/search/HeaderSearch.test.ts

@@ -0,0 +1,110 @@
+/**
+ * The header search bar is the single md+ search input.
+ *
+ * Off /search it navigates there (the only surface that renders results); on
+ * /search it stays put and republishes the query into the URL, so the user goes
+ * on typing in the same box instead of being handed to a second input owned by
+ * the page.
+ *
+ * TRACES: UR-049, UR-054 | DR-147
+ */
+
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { render, screen, fireEvent, waitFor } from "@testing-library/svelte";
+
+const { pageStore, goto, clearSearch } = vi.hoisted(() => {
+  const { writable } = require("svelte/store");
+  return {
+    pageStore: writable({ url: new URL("http://localhost/library/music") }),
+    goto: vi.fn(),
+    clearSearch: vi.fn(),
+  };
+});
+
+vi.mock("$app/stores", () => ({ page: pageStore, navigating: { subscribe: () => () => {} } }));
+vi.mock("$app/navigation", () => ({ goto, afterNavigate: vi.fn(), beforeNavigate: vi.fn() }));
+vi.mock("$lib/stores/library", () => ({
+  library: { subscribe: () => () => {}, search: vi.fn(), clearSearch },
+}));
+
+import HeaderSearch from "./HeaderSearch.svelte";
+
+const afterDebounce = () => new Promise((resolve) => setTimeout(resolve, 450));
+
+function input(): HTMLInputElement {
+  return screen.getByPlaceholderText("Search your library...") as HTMLInputElement;
+}
+
+beforeEach(() => {
+  vi.clearAllMocks();
+  pageStore.set({ url: new URL("http://localhost/library/music") });
+});
+
+describe("from a library route", () => {
+  it("routes to /search with the query and the route's scope", async () => {
+    render(HeaderSearch);
+
+    await fireEvent.input(input(), { target: { value: "jazz" } });
+    await afterDebounce();
+
+    expect(goto).toHaveBeenCalledWith("/search?q=jazz&scope=music");
+  });
+
+  it("clears the results rather than navigating on an empty query", async () => {
+    render(HeaderSearch);
+
+    await fireEvent.input(input(), { target: { value: "jazz" } });
+    await afterDebounce();
+    goto.mockClear();
+
+    await fireEvent.input(input(), { target: { value: "" } });
+    await afterDebounce();
+
+    expect(goto).not.toHaveBeenCalled();
+    expect(clearSearch).toHaveBeenCalled();
+  });
+});
+
+describe("on /search", () => {
+  beforeEach(() => {
+    pageStore.set({ url: new URL("http://localhost/search?q=jazz&scope=music") });
+  });
+
+  it("carries the query over from the URL and puts the caret back in the box", async () => {
+    render(HeaderSearch);
+
+    await waitFor(() => expect(document.activeElement).toBe(input()));
+    expect(input().value).toBe("jazz");
+    expect(input().selectionStart).toBe(4);
+  });
+
+  it("republishes in place instead of pushing a second results screen", async () => {
+    render(HeaderSearch);
+
+    await fireEvent.input(input(), { target: { value: "jazzy" } });
+    await afterDebounce();
+
+    expect(goto).toHaveBeenCalledWith("/search?q=jazzy&scope=music", {
+      replaceState: true,
+      keepFocus: true,
+      noScroll: true,
+    });
+    // The box the user is typing in keeps its text — nothing re-seeds it.
+    expect(input().value).toBe("jazzy");
+  });
+
+  it("searches with the scope the page's chips published, not the route default", async () => {
+    // A chip pick lands in the URL; the bar must adopt it or the next keystroke
+    // would silently widen the search back to All.
+    pageStore.set({ url: new URL("http://localhost/search?q=jazz&scope=tv") });
+    render(HeaderSearch);
+
+    await fireEvent.input(input(), { target: { value: "jazzy" } });
+    await afterDebounce();
+
+    expect(goto).toHaveBeenCalledWith(
+      "/search?q=jazzy&scope=tv",
+      expect.objectContaining({ replaceState: true })
+    );
+  });
+});