Steps 7 and 8: torrents, OPML, and polish

librqbit replaces the vendored BitTorrent 4.2.1 tree. Torrents download
in place because seeding serves the files it downloaded, so the planned
stage-then-move would have broken it. The stall budget now also covers
magnet metadata resolution, which otherwise never returns against a dead
swarm and wedged the scan.

Adds add/rm/import/export, tracing setup, systemd units and README.

A successful swarm download is unverified: no reachable peers here.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01RPyeapneuXrCdojsaiXGbe

contrib/ipx.service

@@ -0,0 +1,18 @@
+# User unit: install to ~/.config/systemd/user/ipx.service, then
+#   systemctl --user enable --now ipx
+# The socket lands in $XDG_RUNTIME_DIR/ipx.sock by default, so a UI running as the
+# same user can attach without extra configuration.
+[Unit]
+Description=ipx podcatcher
+After=network-online.target
+Wants=network-online.target
+
+[Service]
+Type=simple
+ExecStart=%h/.cargo/bin/ipx daemon
+Restart=on-failure
+RestartSec=30
+Environment=IPX_LOG=ipx=info
+
+[Install]
+WantedBy=default.target