fix(schema): escape path.sep before use in RegExp character class on Windows

[LunarLaurus]

Problem

On Windows, path.sep is \ (backslash). When interpolated directly into a RegExp character class:

new RegExp(`^Projects\${path.sep}([^${path.sep}]+)\${path.sep}(.+)$`)

the string passed to RegExp on Windows becomes:

^Projects\([^\]+)\(.+)$

Inside the character class, \] is interpreted as an escaped ] (a literal ] character), so the class [^ never closes — Node throws SyntaxError: Invalid regular expression … Unterminated character class at the point schema.js is first required, which crashes any command that invokes the validator on Windows.

Fix

Escape the separator before building the RegExp, so it is safe in both the character class and the surrounding pattern on all platforms:

const sep = path.sep.replace(/\/g, '\\');
const projMatch = rel.match(new RegExp(`^Projects${sep}([^${sep}]+)${sep}(.+)$`));

• Windows: path.sep = '\' → sep = '\' → regex pattern [^\] (not a backslash) ✅
• POSIX: path.sep = '/' → sep = '/' (no-op) → regex pattern [^/] ✅

Testing

Validated against Notes/*.md belief files on Windows 10 schema validator now returns clean JSON without crashing.