feat(storage): add the encrypted vault, PIN keys, lockout, session and migrations

Records are one ByteArray each: a readable TLV header plus an
encrypt-then-MAC box whose aad binds the entry ID and the header. The
device key seals unlocked entries and pending items; a random master key,
wrapped under a PBKDF2 PIN key, seals locked ones. Wrong PINs are counted
before the check, with delays on the trusted clock and an uptime fallback.
Bytes.toUtf8 validates UTF-8 first, because the native conversion crashes
on invalid input.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

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