feat(store): migration 006 — per-user auto_summarize + per-video summarize_requested

Add the schema for the summarization-mode feature: a per-user auto/manual
toggle (users.auto_summarize, default FALSE = manual) and a per-video manual
queue flag (videos.summarize_requested, default FALSE).

Both columns land on tables that already have ENABLE + FORCE ROW LEVEL
SECURITY (migration 003), so they inherit per-user isolation automatically —
no policy changes needed. auto_summarize is per-user, not global, per ADR-012.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/adapters/store/migrations/006_summarization_mode.down.sql

@@ -0,0 +1,2 @@
+ALTER TABLE videos DROP COLUMN IF EXISTS summarize_requested;
+ALTER TABLE users DROP COLUMN IF EXISTS auto_summarize;

internal/adapters/store/migrations/006_summarization_mode.up.sql

@@ -0,0 +1,17 @@
+-- Migration 006: summarization mode (per-user auto/manual + per-video queue).
+--
+-- auto_summarize is a per-user setting (not a global one): multi-user ready per
+-- ADR-012. FALSE default makes MANUAL the out-of-the-box behavior — `tapir run`
+-- discovers new videos but only summarizes the ones the user explicitly queued.
+--
+-- summarize_requested is the per-video manual queue flag. The web "Summarize"
+-- button sets it TRUE; the next `tapir run` picks it up, summarizes, and clears
+-- it back to FALSE. In auto mode it is unused.
+--
+-- No RLS policy changes needed: both columns are added to tables that already
+-- carry user_id and have ENABLE + FORCE ROW LEVEL SECURITY (migration 003). A new
+-- column on an RLS-protected table inherits that protection automatically — the
+-- existing users_isolation / videos_isolation policies gate every row, so these
+-- columns are only ever readable/writable for the row's own user.
+ALTER TABLE users ADD COLUMN auto_summarize BOOLEAN NOT NULL DEFAULT FALSE;
+ALTER TABLE videos ADD COLUMN summarize_requested BOOLEAN NOT NULL DEFAULT FALSE;