refactor(skills): inline cross-links, drop Related sections, fix conventions

- all nine files: trailing "Related" sections removed, their unique links
  inlined where the topic actually arises (FFI boundary -> c-cpp, embedded
  frontend -> js-typescript, build scripts -> bash, etc.)
- README conventions: rule 2 mandated a Related Skills section, which now
  contradicts practice — replaced with inline-linking and one-home-per-fact
  rules. The <repo>/<rel path> rule was appended after the wrong section
  last commit; moved into the list where it belongs.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

code-languages/csharp-dotnet.md

@@ -143,12 +143,7 @@ interface, a type being renamed):
   project's designated container. Entering one resets the working directory — chain `cd` in the
   same command string.
 - Prefer the project's build script over hand-typed `dotnet` calls; it carries `-warnaserror`,
-  the correct action ordering, and the asset completeness checks.
+  the correct action ordering, and the asset completeness checks — see
+  [`bash.md`](skills-public/code-languages/bash.md) for how that script should be structured.
 - **Never stop, deploy to, or restart an application while the user has it running**, unless
   they have said to.
-
----
-
-## 9. Related
-- [`coding-dev.md`](skills-public/coding-dev.md) — the general rules this extends.
-- [`bash.md`](skills-public/code-languages/bash.md) — for the release pipeline scripts around a .NET build.