feat(core,app,android,cli,ios): sync the library and settings, verify a share before adding it

Sync carried only watch positions, so a second device started empty. The
per-installation history file now also carries per-key registers
(pstr-core::profile): every share with its link and custom password, the
playback, appearance and metadata settings, the TMDB key, hand-picked
matches and per-title track choices. Newer updated_at wins per key, a
removal travels as an empty register, and a first sync stamps at 0 so a
fresh install takes the library the other devices have instead of
overwriting it with defaults. Volume, mute and the device-only settings
(cache budget, Wi-Fi only, background audio, hardware decoding) stay out.
The secrets live only in the end-to-end encrypted Drive file, never in
shares.json. FORMAT_VERSION stays 1; an older build ignores the registers.

Adding a share stored it before opening the link, so a first failure left a
broken entry and every retry said "already configured". add_verified opens
the link first and stores nothing on failure, and only the new share is
crawled afterwards, so another broken share cannot fail the add.

Android drops picture-in-picture: the window sized the video wrongly and
background audio already covers leaving the app.

iOS sizes the Metal drawable on every layout, so the picture no longer
stretches after a rotation or a Split View resize. Settings show a save at
once rather than after the match run, and a failed save reverts and says
why. Both phone clients gain an activity banner naming what is running, and
the add-share, metadata and change-match forms show progress and errors in
place.

ios/ProtonStream/Player/MpvPlayer.swift

@@ -109,6 +109,9 @@ final class MpvPlayer {
     private init() {
         layer.framebufferOnly = true
         layer.backgroundColor = UIColor.black.cgColor
+        // For the frames between a resize and mpv's next one: a drawable of
+        // the old shape is letterboxed rather than stretched.
+        layer.contentsGravity = .resizeAspect
         guard let mpv = mpv_create() else { return }
         // mpv takes the layer's address as an int64, not a Swift reference.
         var wid = Int64(Int(bitPattern: Unmanaged.passUnretained(layer).toOpaque()))