Add folder pickers on Android, iOS, and desktop. Desktop and iOS walk
directory paths in Rust; Android expands SAF trees to per-file FDs
with relative collection paths because directory FDs are unsupported.
Allow selecting multiple files on Android, desktop, and iOS and share them
as one transfer through the core multi-source path. Update the composer UI
for multi-file review, hide unfinished iOS receive methods, and surface
refusal reasons on the receivers list.
Tighten cold-open and in-app invitation handling so ticket acquisition is
stricter and less racey across hosts, and expand automated coverage for the
receive history and acquisition flow before merge.
This adds DeviceInfo to the Platform interface and implements it for Android, iOS, and JVM, including battery level and active network summary where available.
Co-authored-by: Junie <junie@jetbrains.com>
