Relocate three root-level modules into io/, where they belong by concern:
- update_check.rs -> io/update_check.rs (its own doc-comment notes it
mirrors how crate::io wraps blocking calls in async).
- patterns.rs, linetypes.rs -> io/ (standard resource catalogs parsed
from asset files and populated into the document — IO-shaped work).
Fix the moved files' include_str! paths (one level deeper), add the
mod declarations to io/mod.rs, drop them from lib.rs/main.rs, and
re-point all crate:: references to crate::io::. No behavior change.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
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