feat(engine): add opt-in image timeout and scene-paint hedging

IMAGE_TIMEOUT_MS sets a per-attempt hard deadline (AbortSignal.timeout);
IMAGE_HEDGE_MS races a second identical scene-paint request when the
first is still pending past the threshold. Both default to OFF when
unset, preserving historical behavior for self-hosted deploys.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

lib/engine/agents/characterDesigner.ts

@@ -87,7 +87,12 @@ export async function renderCharacterPortrait(
       visualDescription,
       styleGuide,
     );
-    const { imageUrl, imageUuid } = await generateImage(config.image, prompt);
+    // Portraits get the hard timeout but are never hedged — a scene already
+    // runs several portrait paints in parallel, and hedging those would push
+    // burst concurrency past Runware's recommended 2-4 in-flight requests.
+    const { imageUrl, imageUuid } = await generateImage(config.image, prompt, {
+      timeoutMs: config.imageTimeoutMs,
+    });
     return { basePortraitUrl: imageUrl, basePortraitUuid: imageUuid };
   } catch (err) {
     const msg = err instanceof Error ? err.message : String(err);