MeshCore pairing PINs are always six digits, so the PIN dialog now caps input
at six characters and draws a fixed six-slot field: each typed digit shows as a
bullet and each still-blank slot as a muted centre dot (· ), so the field reads
as a row of PIN boxes rather than a growing masked line. _LineEditor gains an
optional max_length (swallows keys past the cap, truncates an over-long paste)
and a slots render mode backing the field.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>