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-tauri/android/src/main/AndroidManifest.xml

@@ -29,6 +29,7 @@
         android:label="@string/app_name"
         android:theme="@style/Theme.jellytau"
         android:hardwareAccelerated="true"
+        android:networkSecurityConfig="@xml/network_security_config"
         android:usesCleartextTraffic="${usesCleartextTraffic}">
         <activity
             android:configChanges="orientation|keyboardHidden|keyboard|screenSize|locale|smallestScreenSize|screenLayout|uiMode|density"

src-tauri/android/src/main/res/xml/network_security_config.xml

@@ -0,0 +1,23 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+  Cleartext HTTP stays blocked everywhere except loopback.
+
+  Downloaded media is served to the webview by a local HTTP server on
+  127.0.0.1 (see media_server.rs / DR-137). Release builds set
+  usesCleartextTraffic="false", so Android's network security policy rejected
+  those requests before any I/O happened and offline video failed instantly with
+  NETWORK_NO_SOURCE.
+
+  Only 127.0.0.1 is exempted. The base config keeps the release default, so a
+  remote server still has to be HTTPS — this must not become a blanket
+  cleartext opt-in.
+
+  TRACES: UR-071 | DR-138
+-->
+<network-security-config>
+    <base-config cleartextTrafficPermitted="false" />
+
+    <domain-config cleartextTrafficPermitted="true">
+        <domain includeSubdomains="false">127.0.0.1</domain>
+    </domain-config>
+</network-security-config>