Scriptor-side companion to 14e-1 (iManager PSR-14 dispatcher +
storage emits). Container now wires a sync dispatcher on top of the
in-memory subscriber provider, hands it to SqliteStorage, and
subscribes two listeners:

Scriptor\Boot\Events\ItemFileCleanupListener
  - Subscribes to ItemDeleted.
  - Walks FileRepository::findByItem() while the row is still
    reachable (Plan §14e contract: dispatcher fires before the SQL
    DELETE so the FK cascade hasn't dropped the metadata yet) and
    asks FileStorage to drop each asset.
  - Also scrubs every <W>x<H>_<file> thumbnail under <dir>/thumbnail/
    via FileStorage::absolutePath() + scandir, matching the upload
    convention (suffix `_<name>` plus a `\d+x\d+_` prefix). Tolerates
    missing dirs and unreadable siblings.

Scriptor\Boot\Events\PageCacheInvalidationListener
  - Subscribes to ItemCreated, ItemUpdated, ItemDeleted.
  - Filters by category id (Pages only — Users mutations don't
    invalidate the rendered-HTML cache).
  - Calls Cache::clear() on the FilesystemCache. BasicTheme keys
    cache entries by md5(host + REQUEST_URI), which we can't recreate
    at event-time, so this is a global flush of the section cache
    until the cache learns tags / per-page prefixes.

ImanagerBootstrap:
  - Registers SubscriberListenerProvider (typed bind) +
    ListenerProviderInterface (alias) + EventDispatcherInterface
    (SyncEventDispatcher composing the provider).
  - SqliteStorage is now built with the dispatcher.
  - wireDomainEventListeners() subscribes both listeners through the
    provider; listener instances are constructed lazily on first
    fire, and the cache-invalidator caches its watched-category id
    after the first lookup so it doesn't re-resolve on every event.

composer.lock: pulls in psr/event-dispatcher 1.0.0 (transitively
through bigins/imanager 14e-1).

Manual smoke (PHP built-in server, fresh PNG fixture):
  POST /editor/pages/edit/      → 302; new item id=11 created
  POST /editor/api/upload       → 200; fileId=5, asset + 300x300
                                  thumbnail on disk
  Frontend hit                  → 1 cache file
  GET /editor/pages/delete/?…   → 302
  Verifications after delete:
    items row gone               (0)
    files row gone               (0; FK cascade)
    asset 14e2.png gone          (ItemFileCleanupListener)
    thumbnail/300x300_14e2.png   gone (ItemFileCleanupListener)
    cache files                  0  (PageCacheInvalidationListener)