fix: gadfly review — video-sized response cap, stale comment

maxVideoResponseBytes (512MB) replaces the shared 64MB JSON cap on the
/v1/videos/sync read path (doRaw now takes the cap per call) — 3/6
models flagged that a legitimate long/high-bitrate clip would be
discarded after minutes of GPU work. Plus a stale stable-diffusion
comment in initImageFilename and a test-handler early return.

Co-Authored-By: Claude Fable 5 <[email protected]>
Claude-Session: https://claude.ai/code/session_01AXQxVhXBw8PwFAtsVrXSmj

provider/llamaswap/video.go

@@ -96,7 +96,7 @@ func (m *videoModel) Generate(ctx context.Context, req videogen.Request, opts ..
 		return nil, fmt.Errorf("llama-swap: build video form: %w", err)
 	}
 
-	videoBytes, contentType, err := m.p.doRaw(ctx, http.MethodPost, "/v1/videos/sync", m.id, w.FormDataContentType(), &buf)
+	videoBytes, contentType, err := m.p.doRaw(ctx, http.MethodPost, "/v1/videos/sync", m.id, w.FormDataContentType(), &buf, maxVideoResponseBytes)
 	if err != nil {
 		return nil, err
 	}
@@ -145,7 +145,7 @@ func initImageFilename(mimeType string) string {
 		return "frame.jpg"
 	case "image/webp":
 		return "frame.webp"
-	default: // stable-diffusion outputs and unknowns: PNG is the safe hint
+	default: // unknown MIME — PNG is the safe hint
 		return "frame.png"
 	}
 }