Sign panel sessions and isolate test runs

- Replace in-memory auth sessions with signed cookies and signed OAuth state
- Add auth route coverage and update panel/web server wiring
- Switch test script to per-file Bun processes and clean up type checks

shared/games/blackjack/blackjack.plugin.ts

@@ -435,7 +435,7 @@ export const blackjackPlugin: GamePlugin<BlackjackState, BlackjackAction> = {
         const isMyTurn = activeId === playerId && state.phase === "player_turns";
         const mySeat = state.seats[playerId];
         const myActiveHand = mySeat && mySeat.activeHandIndex >= 0
-            ? mySeat.hands[mySeat.activeHandIndex]
+            ? mySeat.hands[mySeat.activeHandIndex] ?? null
             : null;
 
         // Determine active hand index for the view
@@ -454,7 +454,7 @@ export const blackjackPlugin: GamePlugin<BlackjackState, BlackjackAction> = {
             myPlayerId: playerId,
             phase: state.phase,
             canAct: isMyTurn,
-            canSplit: isMyTurn && myActiveHand !== null && canSplitHand(myActiveHand, mySeat!.hands.length),
+            canSplit: isMyTurn && myActiveHand !== null && mySeat !== undefined && canSplitHand(myActiveHand, mySeat.hands.length),
             canDoubleDown: isMyTurn && myActiveHand !== null && canDoubleHand(myActiveHand),
             roundNumber: state.roundNumber,
             myCumulativePnl: mySeat?.cumulativePnl ?? 0,