feat: live frame progress streaming for cinematic renders

Replaced communicate() (blocking) with selectors-based line-by-line
stdout streaming — same pattern as still render. Each frame now
streams live to the frontend:

  [cinematic_render] Frame 42/480 -- 55.3s elapsed (0.76 fps)

Pipeline: Blender stdout → log_callback → emit() → Redis →
LiveRenderLog poll (2s) → frontend display

Also added log_callback parameter to cinematic render task call.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

backend/app/domains/pipeline/tasks/render_order_line.py

@@ -479,6 +479,7 @@ def render_order_line_task(self, order_line_id: str):
                         focal_length_mm=focal_length_mm,
                         sensor_width_mm=sensor_width_mm,
                         material_override=override_mat,
+                        log_callback=lambda line: emit(order_line_id, line),
                     )
                     success = True
                     render_log = {