Move the deployment runbook out of the repository into CTXD

By owner directive (2026-10-08), all runbook information lives in the
CTXD project mealquest, file RUNBOOKS.MD, never in the repository.
Delete deploy/RUNBOOK.md, whose content is merged into that CTXD file,
and point the comments in deploy/.env.example, deploy/compose.yaml and
deploy/systemd/mealquest-media-backup.sh at RUNBOOKS.MD instead.

Maestro task e81ed994-a510-48e6-9cf6-e76d5d81f56c.

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

deploy/compose.yaml

@@ -65,8 +65,9 @@ services:
   # the app's own user (owner of the volume) with a read-only root
   # filesystem, no privilege escalation and no Linux capabilities.
   #
-  # Restore: follow "Restore the database" in deploy/RUNBOOK.md (stop the
-  # stack, move the database with its -wal and -shm aside, restore, check).
+  # Restore: follow "Restore the database" in the CTXD project mealquest,
+  # RUNBOOKS.MD (stop the stack, move the database with its -wal and -shm
+  # aside, restore, check).
   litestream:
     image: litestream/litestream:0.5.17
     user: "10001:10001"