Backport from the iOS version: offline downloads, home-first reconnect, stall warning, Close

- Downloads for offline listening: long-press a track, album, artist or
  playlist -> Download; Menu -> Downloads lists them (progress, space used/free,
  play/shuffle, retry, remove). Saved on the SD card (Android/data/com.minamp/
  files/downloads). MP3 originals kept as they are unless above a lower
  download quality; the rest transcoded to MP3 (320 kbps by default). One at a
  time, Range resume for originals, retried when the server is back, Wi-Fi lock.
- Downloaded tracks play from the SD card, offline too; plays made offline
  are reported to Plex when a connection works again.
- Server.pick: when last time's connection was remote, give the plain home
  addresses 2 s first (a hairpinned remote address kept us encrypted and
  capped at home). test/PreferHomeTest.java.
- Playback "playing" but not moving for 12 s: say so instead of staying silent.
- Menu -> Close Minamp: stop the music and close every screen.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

test/PreferHomeTest.java

@@ -0,0 +1,42 @@
+import com.minamp.plex.Server;
+
+/** Server.pick() after being away: the home address wins again when it answers, quickly. */
+public class PreferHomeTest {
+    static int failures = 0;
+
+    static void check(boolean ok, String what) {
+        System.out.println((ok ? "PASS " : "FAIL ") + what);
+        if (!ok) failures++;
+    }
+
+    static Server server(String home, String remote) {
+        Server s = new Server();
+        s.machineId = "abc123";
+        s.add(home, Server.LOCAL_HTTP);
+        s.add(remote, Server.REMOTE);
+        s.sortConnections();
+        s.lastGoodUri = remote;   // last time we were away
+        return s;
+    }
+
+    public static void main(String[] a) throws Exception {
+        String home = "http://127.0.0.1:" + a[0], remote = "http://127.0.0.1:" + a[1], dead = "http://127.0.0.1:1";
+
+        long t0 = System.currentTimeMillis();
+        Server.Conn c = server(home, remote).pick();
+        check(c.kind == Server.LOCAL_HTTP, "back home: home address chosen over last time's remote one (" + (System.currentTimeMillis() - t0) + " ms)");
+
+        t0 = System.currentTimeMillis();
+        c = server(dead, remote).pick();
+        long ms = System.currentTimeMillis() - t0;
+        check(c.kind == Server.REMOTE && ms < 3500, "still away: remote chosen, home check cost " + ms + " ms");
+
+        Server s = server(home, remote);
+        s.lastGoodUri = home;
+        c = s.pick();
+        check(c.kind == Server.LOCAL_HTTP, "home last time: home again");
+
+        System.out.println(failures == 0 ? "ALL PASSED" : failures + " FAILED");
+        System.exit(failures == 0 ? 0 : 1);
+    }
+}

test/identity_server.py

@@ -0,0 +1,15 @@
+"""Answers /identity like a Plex Media Server (for PreferHomeTest). Usage: identity_server.py PORT"""
+import json, sys
+from http.server import BaseHTTPRequestHandler, ThreadingHTTPServer
+
+class H(BaseHTTPRequestHandler):
+    def log_message(self, *a): pass
+    def do_GET(self):
+        body = json.dumps({"MediaContainer": {"machineIdentifier": "abc123"}}).encode()
+        self.send_response(200)
+        self.send_header("Content-Type", "application/json")
+        self.send_header("Content-Length", str(len(body)))
+        self.end_headers()
+        self.wfile.write(body)
+
+ThreadingHTTPServer(("127.0.0.1", int(sys.argv[1])), H).serve_forever()