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>

cli-tooling.md

@@ -180,10 +180,3 @@ system, not scattered at the repository root.
 - **Don't saturate the machine.** A full build consuming every core makes the workstation
   unusable. When something latency-sensitive is running, reduce the job count and `nice` the
   work — and say that you did.
-
----
-
-## 8. Related Skills
-- [`coding-dev.md`](skills-public/coding-dev.md) — writing the code these tools build and test.
-- [`code-languages/bash.md`](skills-public/code-languages/bash.md) — writing the scripts themselves:
-  strict mode, quoting, build-gate structure, destructive-command guards.