Problem

Errors currently surface as Python tracebacks or generic messages with no indication of which .nl file, which line, or what the user should do to fix it.

Acceptance Criteria

• All parse errors include: file path, line number, column (if available), human-readable message
• All resolver/validation errors include the same
• At least one actionable hint per error class (e.g. 'Did you mean X?', 'Missing @use for stdlib.math')
• No raw Python tracebacks visible to end users

Why This Blocks v0.1

Unusable error output means users cannot self-serve. This is the minimum bar for any language toolchain.