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/c-cpp.md

@@ -11,8 +11,8 @@ description: >-
 Extends [`coding-dev.md`](skills-public/coding-dev.md). Everything there applies; this adds C/C++ specifics.
 
 C and C++ are for the cases with no better option: existing codebases, hard real-time paths,
-and FFI boundaries. **For new standalone work, prefer Rust** — the memory-safety guarantees
-are worth more than the familiarity.
+and FFI boundaries. **For new standalone work, prefer [Rust](skills-public/code-languages/rust.md)** — the memory-safety
+guarantees are worth more than the familiarity.
 
 ---
 
@@ -144,10 +144,3 @@ When exposing C/C++ to another language:
 - When a binary search through a packed/embedded blob finds nothing, that is not evidence the
   content is absent — packed asset formats defeat naive string searches. Re-check without
   anchoring before concluding.
-
----
-
-## 9. Related
-- [`coding-dev.md`](skills-public/coding-dev.md) — the general rules this extends.
-- [`rust.md`](skills-public/code-languages/rust.md) — the preferred language for new native work, and the usual consumer
-  of these FFI boundaries.