Removed the eight backward-compat attribute aliases on the orchestrator
(soulseek, youtube, tidal, qobuz, hifi, deezer_dl, lidarr, soundcloud).
External callers and the orchestrator's own internals now reach clients
through the generic alias-aware client(name) accessor.
- core/downloads/{master,monitor,validation}.py: migrated to client().
Monitor's per-source aggregation loop replaced with a single
engine.get_all_downloads() call.
- core/search/{orchestrator,stream}.py: migrated; stream.py drops the
hand-built mode-to-client dict.
- web_server.py: migrated /api/deezer/arl-* + tidal client lookup.
- core/download_orchestrator.py: internal self.soulseek /
self.deezer_dl reaches now route through self.client(); attr
assignments dropped from __init__; module docstring updated.
- Test fakes (_FakeSoulseek, _FakeSoulseekWithYT) expose client(name)
instead of stuffing per-source attributes.
- Conformance test re-pinned to the client() accessor contract.
19 parametrized tests pin every registered plugin class's
structural conformance to DownloadSourcePlugin: every required
method present + async-ness matches the protocol. Drift in any
source fails at the test boundary instead of at runtime against
a live download.
Class-level checks (not instance-level) — instantiating real
clients in fixtures pollutes module state via tidalapi etc.
imports and breaks downstream tests.
