Document the operational routine + ship automation templates

Until opencode session-stopping hooks land upstream, mempalace-session
is the entire mechanism that gets opencode conversations into the
palace — skip it and session history stays trapped in a local SQLite
DB, invisible to semantic search. Previous docs covered setup well
but were thin on when and how often to run it.

- ARCHITECTURE.md §5: replace the one-line 'When to re-mine' note with
  a full Operational Routine section — triggers, cadence, relationship
  to the session lifecycle, automation pointers, verification.
- SKILL.md: add an Operational Routine section aimed at agents —
  when to suggest invoking the tool, cadence guidance, how to
  distinguish this producer-side tool from the consumer-side
  mempalace skill's in-session habits.
- README.md: add 'Keeping it fresh' subsection pointing at contrib/
  and the full docs.

contrib/ ships three ready-to-use templates:
- systemd/mempalace-session.{service,timer} — user units with weekly
  Mon 03:00 schedule, Persistent=true catch-up, RandomizedDelaySec for
  fleet-wide jitter, ConditionPathExists guard for opencode-less boxes,
  Nice+IOSchedulingClass=idle so it never fights interactive work.
- cron/mempalace-session.cron — sample crontab entry with log
  redirection and clear USER-substitution instructions.
- README.md with install/verify/uninstall recipes for both, a chooser
  table (systemd vs cron), container/devbox caveats, and tuning notes
  (daily vs weekly vs monthly trade-offs).

The user's LATER-list item 'wrap mempalace-session in cron/systemd
timer for true auto-save coverage' is now actionable: a single
systemctl --user enable --now command stands it up.

contrib/systemd/mempalace-session.service

@@ -0,0 +1,23 @@
+[Unit]
+Description=Mine opencode session history into MemPalace
+Documentation=https://gitea.jordbo.se/joakimp/mempalace-toolkit
+# Only run if opencode has actually been used (avoids noise on idle machines)
+ConditionPathExists=%h/.local/share/opencode/opencode.db
+# Don't start if a previous run is still going
+ConditionPathExists=!%t/mempalace-session.lock
+
+[Service]
+Type=oneshot
+# The wrapper writes to ~/.cache/mempalace-session/ and the palace.
+# Keep stdout/stderr in the journal — inspect with:
+#   journalctl --user -u mempalace-session --since today
+ExecStart=%h/.local/bin/mempalace-session
+# Belt-and-braces lock so two overlapping runs can't corrupt staging
+ExecStartPre=/bin/sh -c 'touch %t/mempalace-session.lock'
+ExecStopPost=/bin/sh -c 'rm -f %t/mempalace-session.lock'
+# Protect against runaway runs (the 60-session reference mine takes ~21 min;
+# give 2h of headroom for larger corpora and slow disks)
+TimeoutStartSec=7200
+# Low priority — this is background maintenance
+Nice=10
+IOSchedulingClass=idle

contrib/systemd/mempalace-session.timer

@@ -0,0 +1,16 @@
+[Unit]
+Description=Weekly opencode → MemPalace session mine
+Documentation=https://gitea.jordbo.se/joakimp/mempalace-toolkit
+
+[Timer]
+# Every Monday at 03:00 local time. Adjust to taste.
+# Use `systemctl --user list-timers mempalace-session.timer` to see next run.
+OnCalendar=Mon 03:00
+# If the machine was off at the scheduled time, run at next boot.
+Persistent=true
+# Randomize up to 30 minutes to avoid thundering-herd across machines.
+RandomizedDelaySec=30m
+AccuracySec=1m
+
+[Install]
+WantedBy=timers.target