Persist a defaultAccountId preference (SettingsRepository/AppSettings,
following the existing key/field/setter pattern), add a "Default account"
switch to AccountSettingsScreen, and prefer it in ComposeViewModel's
from-account fallback (fromAccountId -> valid default -> first account).
Deleting the default account clears the preference (SettingsRepository
.clearDefaultAccountId), and a stale/foreign id is validated against the
current account list before use so it can never crash or point at a
missing account.
Closes#163
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
JMR-devandClaude Opus 4.8
e06054afb6