feat(rust): slash commands and the next wipe, server half (phase 16)

Five read-only commands registered with api.registerSlashCommands:
/status, /wipe, /top, /online and /clan (D126). Every refusal is private,
and any answer narrower than public (online names, a clan roster) goes
to the caller alone (D127). No command asks a sidecar.

The next wipe (D128, D130): six nullable columns on rust_servers, a pure
nextWipe(row, now) with the zone arithmetic through Intl, computed on
every read. The public server shape gains nextWipe; the admin shape
gains the stored schedule; PUT /admin/rust/servers/:id takes the six
fields and writes them only when wipeRule is present.

server/commands joins ci/bundle.json, which checkBundle caught.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

server/test/servers.test.js

@@ -97,7 +97,7 @@ test('the public shape carries nothing about the sidecar', () => {
   // someone who did not read this file, and an allowlist is the only assertion
   // that catches one.
   assert.deepStrictEqual(Object.keys(shaped).sort(), [
-    'hostname', 'id', 'lastSeenAt', 'level', 'maxPlayers', 'name', 'online', 'players', 'seed', 'stale',
+    'hostname', 'id', 'lastSeenAt', 'level', 'maxPlayers', 'name', 'nextWipe', 'online', 'players', 'seed', 'stale',
     'updatedAt', 'wipeId', 'wipedAt', 'worldSize',
   ])
 })