fix(web/session): preload cast so parse runs at mount, not click

Without preload:true the player only parses the recording when the
user first clicks play. Any parse error during that lazy step
bypasses our lifecycle instrumentation (we only see "ready", which
just means UI mounted), and from the user's POV the play button
stays black because they never see the actual failure.

Forcing preload makes the driver's init() run synchronously-ish with
the "ready" dispatch, so getDuration() resolves to a real number
(or we see an "errored" event with a payload that tells us why).

decnet_web/src/components/SessionDrawer.tsx

@@ -148,7 +148,14 @@ const SessionDrawer: React.FC<SessionDrawerProps> = ({ decky, sid, fields, onClo
       const p = AsciinemaPlayer.create(
         { data: cast },
         playerContainer.current,
-        { fit: 'width', terminalFontSize: '12px' },
+        {
+          fit: 'width',
+          terminalFontSize: '12px',
+          // Force parse up front. Without this the recording is only
+          // parsed on the user's click-to-play, and any parse failure
+          // there is invisible to our lifecycle instrumentation above.
+          preload: true,
+        },
       );
       playerInstance.current = p;
       // The player's init() is async; any failure there bypasses the