feat(render #36): real per-tier output height (360/540/720/1080/4K)

r_height was hardcoded 1080. render-svc now derives r_height from the resolution
(ResolutionHeight) on job create; node-agent ffmpeg downscales to the tier height
(scale=-2:H). Quality picker now actually changes output size.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

services/node-agent/internal/runner/runner.go

@@ -187,7 +187,25 @@ func ffmpegPath() string {
 
 // transcodeToMP4 converts a lossless AE render (AVI/MOV) to a web-playable H.264
 // MP4 using ffmpeg. Returns the .mp4 path. Errors if ffmpeg is unavailable.
-func transcodeToMP4(ctx context.Context, src, requested string) (string, error) {
+// resolutionHeight maps a quality-tier label to its output height (mirrors render-svc).
+func resolutionHeight(resolution string) int {
+	switch strings.ToLower(strings.TrimSpace(resolution)) {
+	case "360p":
+		return 360
+	case "540p":
+		return 540
+	case "720p":
+		return 720
+	case "1080p", "fullhd":
+		return 1080
+	case "4k", "2160p":
+		return 2160
+	default:
+		return 0 // unknown → no scaling
+	}
+}
+
+func transcodeToMP4(ctx context.Context, src, requested string, height int) (string, error) {
 	ff := ffmpegPath()
 	if ff == "" {
 		return "", fmt.Errorf("ffmpeg not found (set FFMPEG_PATH or place ffmpeg.exe next to the agent)")
@@ -196,10 +214,16 @@ func transcodeToMP4(ctx context.Context, src, requested string) (string, error)
 	args := []string{
 		"-y", "-i", src,
 		"-c:v", "libx264", "-preset", "medium", "-crf", "20", "-pix_fmt", "yuv420p",
+	}
+	// Downscale (or up) to the selected quality tier. -2 keeps width even & aspect.
+	if height > 0 {
+		args = append(args, "-vf", fmt.Sprintf("scale=-2:%d", height))
+	}
+	args = append(args,
 		"-c:a", "aac", "-b:a", "192k",
 		"-movflags", "+faststart",
 		dst,
-	}
+	)
 	log.Printf("[ffmpeg] %s %v", ff, args)
 	cmd := exec.CommandContext(ctx, ff, args...)
 	cmd.Stdout = os.Stdout
@@ -281,7 +305,7 @@ func aeRender(ctx context.Context, aePath string, job *Job, outputPath string, o
 			}
 			// Transcode the lossless render → H.264 MP4 (much smaller, web-playable).
 			_ = onProgress(ctx, 92, "Transcoding to MP4…")
-			mp4, terr := transcodeToMP4(ctx, actual, outputPath)
+			mp4, terr := transcodeToMP4(ctx, actual, outputPath, resolutionHeight(job.Resolution))
 			if terr != nil {
 				// ffmpeg missing/failed — fall back to the raw render so the job
 				// still delivers a file (large, but valid).