refactor: move resource/IO root modules under io/

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>

src/lib.rs

@@ -6,13 +6,10 @@ pub mod cli;
 pub mod command;
 pub mod entities;
 pub mod io;
-pub mod linetypes;
 pub mod modules;
 pub mod plugin;
-pub mod patterns;
 pub mod scene;
 pub mod snap;
 pub mod ui;
 pub mod par;
 pub mod sys;
-pub mod update_check;