perf(booth): optimize assets and result flow

WebP reduces UI payload; JPEG keeps portrait saves compatible.\nFinish ends the visit without prompting another portrait.

lib/ai/orchestrator.ts

@@ -41,7 +41,7 @@ export async function orchestrateGeneration(
     // Simulate generation delay (2 seconds)
     await new Promise((r) => setTimeout(r, 2000));
     return {
-      imageUrl: style.sampleResult || style.thumbnail || "/assets/styles/sample_clay_pink.png",
+      imageUrl: style.sampleResult || style.thumbnail || "/assets/styles/jack_o_lantern_sensei.webp",
       providerUsed: "demo_mock",
       modelUsed: "demo-simulator",
       durationMs: Date.now() - startTime,