Fix web client interaction and layout bugs

Placing a card locked the turn in: the chosen card left the hand and no
affordance reverted the placement, forcing the move through. Clicking the
chosen destination again or pressing Escape now steps the selection back.

A failing ONNX inference left the AI's turn unadvanced, permanently
stalling the game. The AI turn now falls back to the heuristic policy.

Other fixes: the score plaque no longer covers hand cards (plaques become
compact chips at narrow widths and hand spacing tracks the viewport),
opponent cards drawn from a discard pile render face up, long expedition
stacks stay inside their lane, undo no longer bumps the generation counter
on empty history, and small viewports scroll instead of clipping.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01LmyprzuzanXRhpomc3Ga1i

web/src/model/policy.ts

@@ -40,7 +40,7 @@ class OnnxPolicy implements Policy {
   }
 }
 
-class HeuristicPolicy implements Policy {
+export class HeuristicPolicy implements Policy {
   readonly provider = "heuristic" as const;
 
   async action(state: GameState): Promise<number> {
@@ -100,3 +100,10 @@ export function loadPolicy(): Promise<{ policy: Policy; warning?: string }> {
   policyPromise ??= initializePolicy();
   return policyPromise;
 }
+
+let heuristicFallback: HeuristicPolicy | undefined;
+
+export function fallbackHeuristicPolicy(): HeuristicPolicy {
+  heuristicFallback ??= new HeuristicPolicy();
+  return heuristicFallback;
+}