feat(render B2): render binder writes user edits into AE before render

Edits previously never reached the MP4 (the node rendered template defaults). Now:
- render-svc claim includes the saved input values as bindings (GetRenderBindings →
  saved_scene_contents with non-empty value).
- node-agent: new binder.go emits a JSON bind-spec + downloads media locally, runs the
  pre-existing data-driven bind.jsx via afterfx (sets text layers' Source Text, replaces
  media footage), saves a bound.aep next to the template, then aerender renders THAT.
- 12-min timeout + fresh-AE + done-marker polling (mirrors scan). Non-fatal: on bind
  failure the job still renders template defaults.

Verified binding data flows (edited frl_c1t1/frl_c1t2 → claim bindings). Live MP4
verification needs the updated node-agent.exe re-run.

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

services/render/internal/db/db.go

@@ -646,6 +646,31 @@ func (s *Store) GetTemplateCompName(ctx context.Context, originalProjectID uuid.
 	return *comp, nil
 }
 
+// GetRenderBindings returns the user's edited input values for a saved project so the
+// node can write them into the AE project before rendering (the render binder). Only
+// inputs with a non-empty value are returned (defaults are already in the template).
+func (s *Store) GetRenderBindings(ctx context.Context, savedProjectID uuid.UUID) ([]models.RenderBinding, error) {
+	rows, err := s.pool.Query(ctx, `
+		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 <> ''`,
+		savedProjectID)
+	if err != nil {
+		return nil, err
+	}
+	defer rows.Close()
+	var out []models.RenderBinding
+	for rows.Next() {
+		var b models.RenderBinding
+		if err := rows.Scan(&b.Key, &b.Type, &b.Value); err != nil {
+			return nil, err
+		}
+		out = append(out, b)
+	}
+	return out, rows.Err()
+}
+
 func (s *Store) CreateExportForJob(ctx context.Context, jobID uuid.UUID) (*models.Export, error) {
 	// Look up the job to get tenant/user/project context
 	job, err := s.getJobByIDInternal(ctx, jobID)