feat(store): migration 018 -- uploaded_transcripts.had_video

Up and down are one commit: golang-migrate pairs them. RLS is unchanged: the
column is on the already-FORCE'd table, so the exact-set isolation test still
holds.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/adapters/store/migrations/018_uploaded_transcripts_had_video.down.sql

@@ -0,0 +1 @@
+ALTER TABLE uploaded_transcripts DROP COLUMN had_video;

internal/adapters/store/migrations/018_uploaded_transcripts_had_video.up.sql

@@ -0,0 +1,9 @@
+-- Migration 018: record whether an uploaded file carried a video track (ADR-033,
+-- amended 2026-10-01).
+--
+-- A Teams meeting with the camera off is still an .mp4 with a video track, so video
+-- files are ACCEPTED: only the audio is extracted and the video is discarded. This
+-- flag lets the transcript page say so — "this file contained a video track; only its
+-- audio was used" — so the user is never left to wonder what happened to the picture.
+-- It outlives the job: completing or failing an upload does not clear it.
+ALTER TABLE uploaded_transcripts ADD COLUMN had_video BOOLEAN NOT NULL DEFAULT FALSE;