feat: improve webtorrent fallback reliability

- Increased `PROBE_TIMEOUT_MS` in `js/gridHealth.js` to 20s to reduce false negatives in peer detection.
- Relaxed the peer check in `js/app.js` to allow forcing a switch to WebTorrent even if the liveliness checker reports 0 peers (showing a warning instead of an error).
- Added `tests/verify_app_switch.mjs` to validate the UI logic change.

js/app.js

@@ -497,12 +497,13 @@ class Application {
 
             if (source === "torrent" && hasActivePeers === false) {
               userLogger.warn(
-                "[app] Unable to switch to torrent playback: no active peers.",
+                "[app] Switching to torrent playback despite 0 active peers detected.",
               );
-              this.showError(
-                "Torrent playback is unavailable right now because there are no active peers.",
+              this.showStatus(
+                "Warning: No peers detected. Playback may fail or stall.",
+                { autoHideMs: 5000 }
               );
-              return;
+              // Proceed anyway
             }
 
             if (source === "url" && cdnUnavailable) {

js/gridHealth.js

@@ -212,7 +212,7 @@ function queueProbe(magnet, cacheKey, priority = 0) {
 }
 
 const PROBE_CACHE_TTL_MS = 5 * 60 * 1000;
-const PROBE_TIMEOUT_MS = 8000;
+const PROBE_TIMEOUT_MS = 20000;
 const PROBE_CONCURRENCY = 96;
 const PROBE_POLL_COUNT = 3;
 const PRIORITY_BASELINE = 1_000_000;