fix(deploy): fix render-worker build context + migration 040 idempotency

- docker-compose.yml: change render-worker build context from ./render-worker
  to . (project root) so pyproject.toml is accessible; update dockerfile path
- render-worker/Dockerfile: update COPY paths for new build context;
  install Python 3.11 via deadsnakes PPA (Ubuntu 22.04 ships 3.10 which
  fails the >=3.11 requirement in pyproject.toml)
- 040_media_assets.py: rewrite upgrade() with raw idempotent SQL (CREATE TYPE
  inside DO $$ EXCEPTION WHEN duplicate_object $$; CREATE TABLE IF NOT EXISTS;
  CREATE INDEX IF NOT EXISTS) to handle pre-existing enum from partial runs

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

docker-compose.yml

@@ -114,8 +114,8 @@ services:
 
   render-worker:
     build:
-      context: ./render-worker
-      dockerfile: Dockerfile
+      context: .
+      dockerfile: render-worker/Dockerfile
       args:
         - BLENDER_VERSION=${BLENDER_VERSION:-5.0.1}
     environment: