[video-engine] Per-project video_engine_enabled opt-in toggle

Mirrors ci_watch_enabled (migration 048): the global
ROBOCO_VIDEO_ENGINE_ENABLED flag arms the subsystem; the new
projects.video_engine_enabled column (migration 063) opts a repo into
authoring against its motion/ dir. VideoEngine._opted_in_project no-ops
open_video_task at the single chokepoint covering all three trigger
paths (on-release, on-spotlight, CEO on-demand) until the operator
flips it in the panel edit-project dialog. Existing projects stay
opted out (server_default=false).

alembic/versions/063_video_engine_project_toggle.py

@@ -0,0 +1,42 @@
+"""Per-project video-engine opt-in column.
+
+The video engine is armed by the global ``ROBOCO_VIDEO_ENGINE_ENABLED`` flag,
+but authoring writes a HyperFrames composition into a project's ``motion/``
+dir, so a project opts in via ``video_engine_enabled``. Additive and
+default-off, mirroring ``ci_watch_enabled`` (migration 048): existing projects
+keep today's behavior (no video authoring) until the operator flips it in the
+panel.
+
+Revision ID: 063_video_engine_project_toggle
+Revises: 062_tiktok_credentials
+Create Date: 2026-07-06
+
+NOTE: revision id is 25 chars — alembic's ``alembic_version.version_num`` is
+``VARCHAR(32)`` and a longer id raises at record time.
+"""
+
+from __future__ import annotations
+
+import sqlalchemy as sa
+from alembic import op
+
+revision = "063_video_engine_project_toggle"
+down_revision = "062_tiktok_credentials"
+branch_labels = None
+depends_on = None
+
+
+def upgrade() -> None:
+    op.add_column(
+        "projects",
+        sa.Column(
+            "video_engine_enabled",
+            sa.Boolean(),
+            nullable=False,
+            server_default=sa.false(),
+        ),
+    )
+
+
+def downgrade() -> None:
+    op.drop_column("projects", "video_engine_enabled")