Legacy v1 instances without an account had no import path after the
switch to explicit account review. Surface them in a separate "Sources"
section of the legacy import view where they can be added with a single
tap (no sign-in) or removed, mirroring the accounts flow. Instances tied
to an account stay in the Accounts section and are not duplicated.
Detection now gates the entry points and first-launch prompt on any
legacy data (accounts or sources), not accounts alone.
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.
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.
