feat(rust): site-owned permissions — the site is the author, the game is the cache

R2, and the first phase where this module WRITES to a game. Groups and grants are
authored on the website and pushed into each server's own permission store, so
every plugin that already calls `UserHasPermission` honours them with no adapter,
and a wipe stops being a data-loss event.

**Seven org-lead decisions (D28-D34).** A grant is keyed to the website USER and
resolved to every Steam id they have linked at push time (D28); every authored row
carries a scope — a server or `*` (D29); groups are mirrored as real groups rather
than flattened (D30); a holder the site did not author is REPORTED, never undone,
with adopt and revoke offered (D31); one verb, with the plugin diffing locally
(D32); a permission no server has registered is reported unresolved and never
self-registered (D33); authoring is people and groups by hand, with rules deferred
(D34).

**Three sets, and every interesting question is a difference between two.**
`desired − pushed` is what to apply; `pushed − desired` is what to RETIRE, because
the site put it there and has since withdrawn it; `present − desired` is drift. The
middle one is why `rust_perm_pushed` exists: a name in the store that is not in the
desired set is either something the site retired or something a human granted, and
those two have opposite correct answers.

**What lands is not what was sent.** A grant naming a permission the server has not
registered did not land — `GrantUserPermission` no-ops silently — and a member the
store has never seen could not be placed. Neither is recorded as pushed, so the
site never believes it gave a privilege it did not.

The loop asks a cheap question every thirty seconds — does the digest of the
desired set still equal what this server last confirmed — and syncs on a change, a
restart, a wipe, a drift hook, a failed attempt past its backoff, or the
fifteen-minute audit that finds drift on a server nobody has touched.

**This module's first admin page**, because a permission model is the first thing
here that has to be composed rather than configured. What is on it is decided by
what an operator can get wrong: four states are invisible from the game and from a
list of grants, and each is a sentence rather than a number.

Walked end to end against a real core at the pinned ref, the real sidecar, and a
stand-in speaking protocol 4 — including a restart that emptied the store and was
fully re-pushed. Four defects the browser found that 133 green tests did not.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PMH6bw1jXMgbyF3ZWGEzSM

server/test/catalogue.test.js

@@ -87,13 +87,13 @@ test('every kind is classified exactly once', () => {
   assert.equal(seen.size, catalogue.PUBLIC_KINDS.length + catalogue.STAFF_KINDS.length)
 })
 
-test('the classification covers exactly the kinds protocol 3 defines', () => {
+test('the classification covers exactly the kinds protocol 4 defines', () => {
   // The spec lives in another repository, so the list is restated here rather
   // than parsed — and restating it is the point: adding a kind to the protocol
   // without deciding who may see it has to fail somewhere, and this is where.
   //
   // Sourced from docs/rust-link/PROTOCOL.md §8.4.
-  const PROTOCOL_3 = [
+  const PROTOCOL_4 = [
     'player.connected',
     'player.disconnected',
     'player.respawned',
@@ -111,7 +111,8 @@ test('the classification covers exactly the kinds protocol 3 defines', () => {
     'server.shutdown',
     'account.link.requested',
     'account.unlinked',
+    'perm.drift',
   ]
 
-  assert.deepEqual([...catalogue.ALL_KINDS].sort(), [...PROTOCOL_3].sort())
+  assert.deepEqual([...catalogue.ALL_KINDS].sort(), [...PROTOCOL_4].sort())
 })