Introduces shared seams for paginated views, D-pad reorder, media control
routing, async singletons and the device method channel, then points the
open-coded copies at them.
Also removes unused models and duplicated provider/server plumbing, folds
the twice-implemented artifact store in the server, and factors the
repeated Flutter toolchain prologue in CI into a composite action.
FFmpeg's protocol lookup is case-sensitive, so a stored "Https://" base
URL reaches mpv verbatim through the direct-play string concat and fails
with "Protocol not found" (API calls survive because Dart's Uri
lowercases the scheme). Canonicalize at Jellyfin URL intake and in the
connection constructor so persisted configs self-heal on load, and
register mpv-escaped (https\://) redaction variants so option-value
logs stop leaking the server host.
close#1465
edde746