Removed the unused ``news.subscription_manager`` storage subsystem
(``SQLSubscriptionStorage``, ``SearchSubscription``, ``TopicSubscription``,
``BaseSubscription`` and their factories), the abstract ``SubscriptionStorage``
interface, and ``StorageManager.get_user_subscriptions`` /
``get_user_stats``. This code was never reached by any live path -- all real
subscription functionality goes through ``news.api`` and the scheduler -- and
was broken against the current ``NewsSubscription`` model (it referenced
columns such as ``user_id``/``refresh_count``/``results_count`` that do not
exist, so it raised ``AttributeError`` whenever called). The package-level
exports ``SearchSubscription`` and ``TopicSubscription`` from
``local_deep_research.news`` are removed as part of this; nothing in the
codebase imported them.
