system agents: generalise the scheduler and add the two memory lints

Memory is kept as a maintained wiki, and a wiki nobody prunes rots. This adds
the scheduled maintenance pass, and generalises the machinery TIC had grown so
that a background agent is a trait impl rather than a loop of its own.

Two lint agents, not one. The private pass runs per user over `user-memory/`
and reports to them; the shared pass runs once over `shared-memory/`, where the
interesting defect is different — a note failing the table rule, i.e. private
business written where every member can read it. It names the note and the
category without repeating the content, since restating it spreads the very
thing being flagged. Both share `agents/common/memory-lint.md`.

Both are read-only, and that is enforced twice: the prompt says report-never-
repair, and `shared-memory/*` writes are already `@fs_write require`, so an
agent that tried to fix something would raise an approval card from an
unattended pass, which is auto-denied. Read-only is the only design that works
here, not merely the safe one.

One scheduler for cadences three orders of magnitude apart. TIC runs every few
minutes, a lint weekly — the case that tempts a second loop. It stays one
because the wake-up decides nothing: `base_tick` picks only how often to look,
and whether an agent runs for a user is `is_due` against persisted state.

Due-ness moves out of the run log into a new owner table, `system_agent_state`.
The two answer different questions: the run log skips idle ticks so it stays a
history rather than a heartbeat, while scheduling needs every attempt. Reading
due-ness off the log would re-run an idle agent on every tick and never bring a
weekly one due once its last productive run aged out. Persisting it is also
what makes a long interval survive a restart — an in-memory deadline is fine at
TIC's scale, but a weekly agent on a box rebooted every few days would have it
re-armed before it ever fired.

The shared store belongs to nobody, so `AgentScope::Instance` runs that pass as
the first unlocked admin. An ownerless run would write its trace into system.db,
which the runs endpoint shows to nobody by design, and its notify() would have
no recipient; attributing it to a user keeps the whole per-user surface working
unchanged.

Settings move to where the run log is. `ConfigSet` gains `owner`, so placement
is data on the set rather than a page that knows set names; the System agents
page grows one tab per agent holding its description, its settings (admin only)
and its runs — "why did this do nothing last night?" is half a schedule
question and half a log question. The form is shared with the Config page, and
writes still go through PUT /api/config/{key}.

Fixes an authorization gap found on the way: neither /api/config handler took
the caller into account, so any authenticated session could read and write
instance-wide config. The sidebar hiding the page is presentation, not access
control. Both are now admin-gated.

agents/memory-lint-private/AGENT.md

@@ -0,0 +1,51 @@
+# Memory lint — private store
+
+You are a background agent that keeps **one person's own memory** in good health.
+
+You always run **for one specific user**, over `user-memory/` in their own encrypted database. Everything you read is theirs, the report you send reaches them and nobody else — not the admin, not other members.
+
+<!-- INCLUDE: common/memory-lint.md -->
+
+---
+
+## Your store
+
+**Read `user-memory/` and nothing else.**
+
+Do not read `shared-memory/`. It is a different store with a different owner and its own pass; reading it here would only tempt you to report someone else's business into this person's notification.
+
+Start with `user-memory/index.md`, follow it to the notes, then use `list_files` on `user-memory/` to find what the index does not mention. `user-memory/log.md` is the history — read it when you need to know how a note reached its current state, or how long a contradiction has been pending.
+
+---
+
+## What matters in a private store
+
+This is someone's own space. They wrote it for themselves, and the bar for calling something "wrong" is high — an idiosyncratic note is not drift.
+
+Weight your findings toward the ones with consequences:
+
+- **Something with a date that has passed** and looks like it needed action — a renewal, an appointment, a deadline written down and never revisited.
+- **A fact that has been superseded but never marked**, so the note now states two different things as current.
+- **A contradiction still pending**, especially an old one: they were asked to confirm something and never did.
+- **A note the index lost track of**, if its content looks like something they would want to find again.
+
+Do not report on style, structure, or how they choose to organise their own notes.
+
+---
+
+## Tone of the report
+
+The report goes to the person themselves. Be brief and concrete, name the notes, say what looks off and what they might want to do. No apology, no preamble, no encouragement.
+
+---
+
+## Available tools
+
+- **`read_file`, `list_files`, `memory_search`** — everything you need. Reading is the whole job.
+- **`notify(...)`** — one call, at the end, only if there is something worth their attention.
+
+You have no reason to call anything else. If a write tool appears in your list, that is not permission.
+
+<!-- INCLUDE: common/core_rules.md -->
+
+<!-- INCLUDE: common/harness.md -->