feat(render): node-agent AE snapshot runner (Epic C2) + colour render-binding (Epic B)

C2 — real-AE scene snapshots on the node:
- node-agent: runner/snapshot.go RunSnapshot (aerender -comp <key> -s f -e f
  → findRenderedOutput → ffmpeg -frames:v 1 PNG); client ClaimSnapshot /
  GetSnapshotUploadURL / ReportSnapshotResult / ReportSnapshotFail; snapshotLoop +
  pollSnapshotOnce mirroring the scan loop (reuses the AE-exclusive lock).
- render-svc: GetSnapshotJobMeta + UploadURL handler presigns a PUT to the
  public-read user-uploads bucket at snapshots/{project}/{scene}.png and returns a
  permanent public_url (not the time-limited export presign); MINIO_UPLOAD_BUCKET +
  MINIO_PUBLIC_URL config + compose env + /snapshot/:id/upload-url route.

Epic B — bind edited colours into the render:
- render-svc GetRenderBindings UNIONs studio.saved_shared_colors +
  saved_scene_colors (type 'color') so the node writes them before render.
- node-agent binder.go routes type:"color" bindings into the bind-spec colors[]
  array that bind.jsx already applies to the frshare colour layers.

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

services/render/internal/db/db.go

@@ -674,7 +674,19 @@ func (s *Store) GetRenderBindings(ctx context.Context, savedProjectID uuid.UUID)
 		SELECT c.key, c.type, COALESCE(c.value, '')
 		FROM studio.saved_scene_contents c
 		JOIN studio.saved_scenes s ON s.id = c.saved_scene_id
-		WHERE s.saved_project_id = $1 AND c.value IS NOT NULL AND c.value <> ''`,
+		WHERE s.saved_project_id = $1 AND c.value IS NOT NULL AND c.value <> ''
+		UNION
+		-- project-wide shared colours (frshare/frd_* layers): bind.jsx writes these
+		-- into the frshare comp's text layers so template expressions propagate them.
+		SELECT sc.element_key, 'color', sc.value
+		FROM studio.saved_shared_colors sc
+		WHERE sc.saved_project_id = $1 AND sc.value IS NOT NULL AND sc.value <> ''
+		UNION
+		-- per-scene colours (frl_c* layers)
+		SELECT cc.element_key, 'color', cc.value
+		FROM studio.saved_scene_colors cc
+		JOIN studio.saved_scenes s2 ON s2.id = cc.saved_scene_id
+		WHERE s2.saved_project_id = $1 AND cc.value IS NOT NULL AND cc.value <> ''`,
 		savedProjectID)
 	if err != nil {
 		return nil, err

services/render/internal/db/snapshotjobs.go

@@ -123,3 +123,13 @@ func (s *Store) SetSnapshotError(ctx context.Context, id uuid.UUID, msg string)
 		id, msg)
 	return err
 }
+
+// GetSnapshotJobMeta returns the project id + scene key for a job (to build the
+// object key the node uploads its rendered still to).
+func (s *Store) GetSnapshotJobMeta(ctx context.Context, id uuid.UUID) (uuid.UUID, string, error) {
+	var pid uuid.UUID
+	var key string
+	err := s.pool.QueryRow(ctx,
+		`SELECT project_id, scene_key FROM render.snapshot_jobs WHERE id = $1`, id).Scan(&pid, &key)
+	return pid, key, err
+}