fix(webtorrent): stop feed health-probe connection storm (freeze/crash)

The feed's per-card stream-health badges ran WebTorrent swarm probes at
PROBE_CONCURRENCY = 96, and each probe's torrent.add set no maxConns (WebTorrent
default 55 peers). Loading/scrolling the feed could therefore open
~96 x 55 simultaneous WebSocket/WebRTC connections, pegging the main thread
(freeze) and exhausting memory (tab crash); playing a video added the streaming
torrent on top and tipped it over. This also produced the MaxListenersExceeded
warnings and relay/connection storms.

- gridHealth: PROBE_CONCURRENCY 96 -> 4 (probes are real swarm joins, not pings).
- webtorrent probePeers add: maxConns: 4 (a probe only needs to see >=1 peer).
- webtorrent playback add: maxConns: 30 (caps the streaming handshake storm;
  ample for playback bandwidth).

Pre-existing issue (not from the file-size refactor — verified). Confirmed
locally: feed scroll + playback no longer freeze/crash. grid-health +
webtorrent-regression tests pass; build green.

Co-Authored-By: Claude Opus 4.8 <[email protected]>

js/gridHealth.js

@@ -230,7 +230,12 @@ function queueProbe(magnet, cacheKey, priority = 0, webSeeds = []) {
 
 const PROBE_CACHE_TTL_MS = FIVE_MINUTES_MS;
 const PROBE_TIMEOUT_MS = 20000;
-const PROBE_CONCURRENCY = 96;
+// Each probe is a real WebTorrent swarm join (tracker announces + peer
+// connections), NOT a cheap ping. At 96 concurrent, loading/scrolling the feed
+// opened hundreds-to-thousands of simultaneous WebSocket/WebRTC connections,
+// pegging the main thread and exhausting memory (freeze + tab crash). Keep this
+// small — badges still populate, just a few at a time.
+const PROBE_CONCURRENCY = 4;
 const PROBE_POLL_COUNT = 3;
 
 class ProbeQueue {

js/webtorrent.js

@@ -184,6 +184,11 @@ export class TorrentClient {
         const addOptions = {
           announce: trackers,
           maxWebConns: safeMaxWebConns,
+          // A probe only needs to detect that >=1 peer/webseed exists, so cap
+          // peer connections hard. Without this WebTorrent defaults to 55 per
+          // torrent — multiplied across concurrent probes that floods the
+          // browser with connections (freeze/crash).
+          maxConns: 4,
         };
         /**
          * CRITICAL: We pass the webseed URL (if present) to the client via `urlList`.
@@ -933,7 +938,10 @@ export class TorrentClient {
             .filter((entry) => /^https?:\/\//i.test(entry))
         : [];
 
-      const chromeOptions = { strategy: "sequential" };
+      // Cap peer connections for the streaming torrent too. 30 is plenty to
+      // saturate playback bandwidth while avoiding the WebRTC-handshake storm
+      // that can peg the main thread (WebTorrent's default is 55).
+      const chromeOptions = { strategy: "sequential", maxConns: 30 };
       /**
        * CRITICAL: Passing `urlList` ensures the client can stream from the webseed.
        * Without this, videos with 0 P2P peers will fail to play even if a valid