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/models/models.go

@@ -432,6 +432,17 @@ type ClaimedJob struct {
 	// template's render_aep_comp (e.g. "frfinal"). Empty → node falls back to the
 	// project's render queue.
 	CompName string `json:"comp_name,omitempty"`
+	// Bindings are the user's edited input values to write into the AE project before
+	// rendering (the render binder). Key = AE layer/footage name (frl_c{n}{t|m}{i}).
+	Bindings []RenderBinding `json:"bindings,omitempty"`
+}
+
+// RenderBinding is one input value the node writes into the AE project before render:
+// a Text layer's source text, or a Media footage replacement.
+type RenderBinding struct {
+	Key   string `json:"key"`   // AE layer/footage name, e.g. frl_c1t1 / frl_c1m1
+	Type  string `json:"type"`  // content element type (Text, Media, …)
+	Value string `json:"value"` // text content, or a media URL
 }
 
 // OutputUploadURLResponse is returned by POST .../output-upload-url.