feat(modules): event triggers, audiences and the ceiling lattice (engagement Phase 2)

The contract half of the engagement system: a module (and core) can DECLARE an
event with a payload contract and fire it. Nothing delivers yet — `emit`
validates, logs and stops, and Phase 4 replaces that log line with the engine.

`api.registerEventTriggers` and `api.registerAudiences` ride the existing
stage()/apply() validate-then-commit discipline, so a registrant that throws
halfway leaves nothing behind. `ctx.events.emit` is fire-and-forget and binds
the owner from the calling module — a module fires its own triggers and no one
else's. `ctx.inbox.push` is present and throws until Phase 7, the shape 1.6.0
settled on for a member that arrives a phase late.

MODULE_API_VERSION 1.7.0 on both halves. Additions only; module-uo's
`coreApi: "^1.3.0"` still resolves.

Three design decisions, approved by the org lead before any code:

ONE NAMESPACE for trigger ids and notification-stream ids (ENGAGEMENT.md §7.2,
against the recommendation in the text). A trigger is a payload contract
attached to an id that may also carry a subscription toggle, so an id has
exactly one owner across both facets, checked in both directions. Core's five
trigger ids ARE its five stream ids, so the same-owner upgrade case is
exercised on every boot rather than only by a module. It keeps
notification_channel_prefs single-keyed in Phase 3, where two namespaces would
have forced a `kind` discriminator into its primary key.

Two knock-on effects appeared only once it was implemented. The id grammar had
to be RELAXED to admit `_` inside a segment — §4.3's own worked example is
`uo.house.idoc_warning`, and two grammars over one namespace would mean an id
legal as a trigger and illegal as the stream it is the same event as. And the
seven grandfathered `uo.*` ids had to share their legacy allowlist with
triggers, because under one namespace `idoc.warning` is a single id. The push
catalog is untouched either way: allStreams() still serves the stream facet
only, so the shipped Android client sees exactly what it saw before.

THE CEILING LATTICE (G24), which the plan named everywhere and defined nowhere.
It is containment, not size: everyone ⊃ authenticated ⊃ {subscribers, members,
staff, owner}, with the four leaves mutually incomparable. The flat total order
the plan's wording invites would let a `staff`-ceilinged trigger be given an
`owner` audience — a rule that mails cheat detection to the player it detected.
Fewer people is not less exposure. Two incomparable ceilings have no meet at
all, so a composition is refused rather than guessed; union-widens is the
intuitive implementation and it is the wrong one.

`kind: 'event' | 'scheduled'` is declarable now and no evaluator exists (§7.1
Q6). Registration accepts `scheduled` and emit refuses to fire one, so `kind`
means something from the moment it can be written rather than from the moment
it is honoured.

Also: `GET /admin/engagement/{triggers,audiences}`, served from the registries
rather than a table so an uninstalled module simply stops appearing;
`npm run engagement:manifest` plus its CI `--check`, the twin of the route
manifest, because renaming a variable breaks stored templates silently, at send
time, in mail someone already received.

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

server/src/modules/version.js

@@ -9,6 +9,26 @@
 // Deliberately separate from PROTOCOL_VERSION (which versions the shard wire and
 // has nothing to say about a website module) and from any module's own version.
 
+// 1.7.0 — the engagement contract (docs/website/ENGAGEMENT.md Phase 2).
+// Additions only, so minor: `api.registerEventTriggers([...])`,
+// `api.registerAudiences([...])`, `ctx.events.emit(triggerId, envelope)` and
+// `ctx.inbox.push(userId, item)`. module-uo's `coreApi: "^1.3.0"` still resolves.
+//
+// **As in 1.6.0, the number covers the whole surface and the members arrive by
+// phase.** `ctx.inbox.push` is present and THROWS until Phase 7 builds the
+// in-app channel and the table behind it — the same choice, for the same reason:
+// a member of 1.7.0 that were absent would make the version a lie, and one that
+// silently accepted data into a table that does not exist would be worse than
+// either. Everything else in 1.7.0 is live.
+//
+// One thing here is not a member and is still part of the contract: a trigger id
+// and a notification-stream id share ONE namespace (ENGAGEMENT.md §7.2, settled
+// by the org lead in Phase 2). An id has exactly one owner across both facets,
+// so a module cannot attach a payload contract to another module's stream. That
+// tightens a rule rather than changing a signature, and nothing registrable
+// before this bump becomes unregistrable after it — the id grammar was RELAXED
+// in the same change (`_` is now legal inside a segment).
+//
 // 1.6.0 — the Team surface (docs/website/TEAMS.md Part 11). Additions only, so
 // minor: `api.registerTeamProvider({ getTeams, getTeamMembers, getTeamLeaders })`,
 // `ctx.teams.publish(event)`, `ctx.teams.reconcile({ reason })`,
@@ -58,6 +78,6 @@
 // an admin action a module performs belongs in core's one audit log, the
 // extension slot needs the user its prefix names, and §2.7 forbids a module
 // reading core's `APP_BASE_URL` for itself. Additions only, so minor.
-const MODULE_API_VERSION = '1.6.0'
+const MODULE_API_VERSION = '1.7.0'
 
 module.exports = { MODULE_API_VERSION }