feat(workers): ingest.video via yt-dlp + Whisper

yt-dlp pulls metadata (title, description, uploader, thumbnail) and
bestaudio (opus). faster-whisper transcribes; audio file removed after.
Creates a refs row with kind='video' and source_kind='youtube' for
YouTube URLs, generic 'video' otherwise. Idempotent on
sha256(space_id + url) via refs.external_id.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

workers/void_workers/handlers/__init__.py

@@ -1,7 +1,8 @@
-from . import echo, pdf, image
+from . import echo, pdf, image, video
 
 REGISTRY = {
     echo.NAME: echo.handle,
     pdf.NAME: pdf.handle,
     image.NAME: image.handle,
+    video.NAME: video.handle,
 }