feat(studio B1): persist input edits to content elements (render-binding foundation)

Studio edits previously went only to edit_state; the render binds saved_scene_contents,
so edits never reached the MP4. Add studio-svc PATCH /v1/saved-projects/{id}/contents
(update saved_scene_contents.value/value_file_id by content key, ExecuteSqlInterpolated
for null-safe params) + Next /api/projects/[id]/contents route + persistence hook pushes
edited values (from bridged c-<key> layers) alongside the scene_data save. Verified
text persists incl. UTF-8 Persian (9 chars/17 bytes).

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

src/hooks/useStudioProjectPersistence.ts

@@ -9,8 +9,10 @@ import {
   saveLocalProject,
 } from "@/lib/dev-project-storage";
 import {
+  contentValuesFromSceneData,
   fetchProject,
   isProjectNotFoundError,
+  patchProjectContents,
   patchProjectSceneData,
 } from "@/lib/project-api";
 import { isDevProjectId } from "@/lib/project-ids";
@@ -151,6 +153,12 @@ export function useStudioProjectPersistence(
       try {
         const scene_data = JSON.parse(payloadJson) as Record<string, unknown>;
         await patchProjectSceneData(projectId, scene_data);
+        // Persist the per-input values to content elements so the render binder uses
+        // them (best-effort — never block the main save on it).
+        void patchProjectContents(
+          projectId,
+          contentValuesFromSceneData(scene_data)
+        ).catch(() => {});
         setUsingLocalStorage(false);
         markSaved(payloadJson, false);
       } catch (error) {