Adds src/lib/utils/settingsMigrations.ts exposing
loadSettingsWithMigration() / saveSettingsWithVersion() around a
{version, data} envelope in localStorage["kon_settings"]. The
migration chain is indexed by destination version so adding a v2
is one MIGRATIONS[2] = (prev) => next entry away from working.
Legacy bare-object settings blobs are treated as v0 and folded into
v1 identically to before — no user-facing reset — but an unreadable
blob now surfaces a single Settings reset toast instead of silently
dropping data.
Covers Handy #602 ('settings reset on update') and unblocks the
other B.2/B.3 SettingsState additions listed in
docs/whisper-ecosystem/workstream-B.md: every subsequent field
lands behind a MIGRATIONS step, so older Kon builds stay readable.
Co-authored-by: jars <jakejars@users.noreply.github.com>
