Delete declarations that Periphery reports unused on every platform that
compiles them (iOS, macOS, tvOS), including nine views used only by their
own previews. Platform-gated code still used on another platform, device-
only MPV render paths, migration models, CloudKit record names, App
Intents metadata and unused parameters are kept.
The Test Connection buttons only probed API/server reachability, which
was misleading: a green result said nothing about whether videos would
actually play. Remove both the remote-server and WebDAV bandwidth test
buttons and all code exclusive to them (testBandwidth, BandwidthTestResult,
and orphaned localization keys). Add-time connectivity validation for
SMB/WebDAV sources is retained.
