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/_fakes.js

@@ -129,6 +129,7 @@ function fakeApi() {
     routes: null, extensions: [], streams: null, legs: [], hooks: {}, teamProvider: null,
     triggers: null, audiences: null, engagementSeeds: null,
     eventBudgets: null, eventOptionSources: null, eventLeases: null, eventActions: null,
+    slashCommands: null,
   }
   const called = new Set()
   const once = (name) => {
@@ -157,6 +158,8 @@ function fakeApi() {
     registerEventOptionSources(sources) { once('registerEventOptionSources'); record.eventOptionSources = sources },
     registerEventLeases(leases) { once('registerEventLeases'); record.eventLeases = leases },
     registerEventActions(actions) { once('registerEventActions'); record.eventActions = actions },
+    // Core's `once()` holds here too: a module's commands are one batch.
+    registerSlashCommands(commands) { once('registerSlashCommands'); record.slashCommands = commands },
     onBoot(fn) { once('onBoot'); record.hooks.onBoot = fn },
     onShutdown(fn) { once('onShutdown'); record.hooks.onShutdown = fn },
   }