Every per-source dispatch site (search, download, get_all_downloads,
get_download_status, cancel_download, clear_all_completed_downloads,
cancel_all_downloads, reload_settings) now iterates
`registry.all_plugins()` instead of hand-maintained client lists.
Backward-compat `self.soulseek` / `self.youtube` / etc. attributes
preserved as registry-resolved aliases — external callers reaching
for source-specific internals (e.g. `orchestrator.soulseek._make_request`)
keep working unchanged.
Adding a new source (Usenet planned) becomes one registry entry +
the new client class — no orchestrator changes.
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