feat(account): unlink game accounts on the shard before an account is deleted (MODULE_API 1.20.0)

ACCOUNT_DELETION.md §4.4 (AD10, AD11). api.onUserDeleting queues every linked
account in the new shard_pending_unlinks table, then calls the sidecar's
DELETE /link/{account} (actor web:account-deletion) and drops the mirror on 200/404.
A shard that is away leaves the row pending, retried on WS reconnect and on a live
server.hello; a protected account (403) is refused and listed on Admin -> Shard as
still linked on the shard. A live mob.login without the deleted user's webId clears
the row. coreApi ^1.20.0; core-ref pinned to website#232's merge (7bd93b8).

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

server/test/entry.test.js

@@ -131,6 +131,8 @@ test('registers exactly what module.json declares', () => {
   assert.ok(api.record.streams.length > 0)
   assert.strictEqual(typeof api.record.hooks.onBoot, 'function')
   assert.strictEqual(typeof api.record.hooks.onShutdown, 'function')
+  // MODULE_API 1.20.0: a deleted account's game links are unlinked on the shard.
+  assert.strictEqual(api.record.hooks.onUserDeleting, require('../utils/accountDeletion').onUserDeleting)
 })
 
 test('every registered stream is namespaced or grandfathered', () => {