Say in compose that the calendar is off, and why (V-644)

mavcaldav was built, in `make build`, listed in CLAUDE.md's daemon table, and
deployed nowhere. Not commented out the way mavmaild is, which at least
records the decision and the enable steps. Built and mentioned nowhere is the
worst of the three states, so this writes the decision down.

The box has no CalDAV account, so the block stays commented. It names what the
absence costs, because both costs are invisible from the daemon table. Agenda
questions route correctly and answer from nothing: stage 0 sends "что у меня
сегодня" to IntentQuery (V-498) and the calendar query source then reads facts
nobody writes. And loop.State.CalendarBusy is fed by those same facts, so the
gate's "do not nag mid-meeting" is permanently false.

CLAUDE.md said the absence was an oversight. It is a decision now.

docker-compose.yml

@@ -157,6 +157,44 @@ services:
   #     - maildata:/var/lib/mavmaild
   #     - ./deploy/imap.password:/run/secrets/imap.password:ro
 
+  # The calendar reader (Vikunja #644) is OFF and commented out: it needs a
+  # CalDAV account, and there is none on this box. It was built, listed in
+  # `make build`, and deployed nowhere, which is the worst of the three states —
+  # this block records the decision instead.
+  #
+  # What its absence costs, so the cost is visible from here:
+  #   - Agenda questions route correctly and answer from nothing. Stage 0 sends
+  #     "что у меня сегодня" to IntentQuery (V-498) and the `calendar` query
+  #     source reads facts(kind=env, source=caldav:*) that nobody writes.
+  #   - The nudge gate loses a suppressor. loop.State.CalendarBusy is fed by
+  #     those same facts, so "do not nag mid-meeting" is permanently false.
+  #
+  # Core never sees the CalDAV password: the reader polls the collection itself
+  # and hands core one fact per event over WriteFact. Nothing here can create a
+  # reminder, so a misread event cannot fire.
+  #
+  # The password is read from a FILE, so it never appears in `ps`, in this file,
+  # or in shell history — the same rule mavpoll and mavmaild follow.
+  #
+  # To enable: write the password to deploy/caldav.password (0600, gitignored),
+  # point -url at the collection, and uncomment this service. No mavend.json
+  # block is needed — events arrive over IPC as facts. -render-url is optional
+  # and OFF here: it publishes Maven's own reminders back as events, and it must
+  # not name the collection -url reads, or the poller reads its own writes back
+  # in (checkRenderTarget refuses that). It takes -render-pass-file, and falls
+  # back to this password when that is not given.
+  # mavcaldav:
+  #   <<: *image
+  #   command: ["mavcaldav", "-socket", "/run/maven/mavend.sock",
+  #             "-url", "http://localhost:5232/kami/personal",
+  #             "-user", "kami",
+  #             "-pass-file", "/run/secrets/caldav.password",
+  #             "-interval", "5m"]
+  #   depends_on: [mavend]
+  #   volumes:
+  #     - sockets:/run/maven
+  #     - ./deploy/caldav.password:/run/secrets/caldav.password:ro
+
 volumes:
   dbdata:
   sockets: