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.

README.md

@@ -70,6 +70,25 @@ mempalace-docs /workspace/my_project --dry-run
 mempalace-docs /workspace/my_project
 ```
 
+### Keeping it fresh (automation)
+
+Manual invocation is fine while you're actively driving the machine, but long-running devboxes benefit from a weekly automated mine. [`contrib/`](contrib/) ships ready-to-install templates:
+
+- **systemd user timer** (recommended on modern Linux): survives reboots, catches missed runs, logs to `journalctl`.
+- **cron**: simpler, works everywhere, no user-unit awareness needed.
+
+Quick-start (systemd, weekly Mon 03:00 local):
+
+```bash
+mkdir -p ~/.config/systemd/user
+cp contrib/systemd/*.{service,timer} ~/.config/systemd/user/
+systemctl --user daemon-reload
+systemctl --user enable --now mempalace-session.timer
+sudo loginctl enable-linger "$USER"   # optional, for headless boxes
+```
+
+See [`contrib/README.md`](contrib/README.md) for full install/verify/uninstall recipes, tuning, and devbox/container caveats. The full operational routine (triggers, cadence, verification) is in [`ARCHITECTURE.md`](ARCHITECTURE.md) §5.
+
 ### Containerized (devbox) notes
 
 On a Docker-based devbox, the palace and opencode DB should live on named volumes so they survive container recreate: