The manual account-import flow made the old silent instance-import
pipeline unreachable. Drop the orphaned parsing, reachability checks,
batch import, result/error types, and the old import row view, plus the
httpClient dependency they were the only consumer of. Also remove the
LegacyAccount.password field, which was parsed but never read.
Delete the multi-page onboarding sheet. On first launch the app now
silently imports any v1 instances from UserDefaults (splitting embedded
basic-auth credentials out of the URL and into the Keychain) and then,
if the device is signed in to iCloud, shows a single alert offering to
enable sync. Accepting shows a blocking progress overlay until the
initial upload completes.
Adds a "Proxy videos" toggle in instance settings that routes video
streams through the instance instead of connecting directly to YouTube
CDN. Includes auto-detection of 403 blocks and live re-application of
proxy settings without requiring app restart or video reload.
