docs(contributing): clarify which conventions are tool-enforced

Address Copilot review on #407: the Code Style preamble said
conventions are not enforced by tooling, which contradicted the new
note that  enforces the flat file
pattern. Reword the preamble so dylint is acknowledged alongside fmt
and clippy and so the manual-vs-enforced split is consistent across
subsections.

Author: claude

CONTRIBUTING.md

@@ -32,7 +32,7 @@ Write documentation, comments, and other prose for ease of understanding first.
 
 ## Code Style
 
-Automated tools enforce formatting (`cargo fmt`) and linting (`cargo clippy`). The following conventions are **not** enforced by those tools and must be followed manually.
+Automated tools enforce formatting (`cargo fmt`), linting (`cargo clippy`), and a curated set of project-specific rules via dylint (`cargo dylint --all`, run with `DYLINT=true ./test.sh`). The following conventions must be followed manually unless a subsection notes that a specific dylint rule enforces them.
 
 ### Import Organization