feat(auth): support stronger custom access passwords

[dx2331lxz]

Summary

• allow custom public and LAN PINs from 8 to 128 characters
• accept symbols and Unicode characters while rejecting whitespace and control characters
• keep generated PINs as 8-digit numeric values
• update the settings UI, login form, documentation, and regression coverage

Validation

• npm test (178 passing)
• npm run build:client
• git diff --check

The server-side validation remains authoritative; the client only filters disallowed whitespace/control characters for a better input experience.