refactor: remove per-skill README.md (duplicates SKILL.md)

[blafourcade]

Problem

Each skill ships a README.md that duplicates the SKILL.md ~100% (when-to-use, when-not-to-use, actions table, invocation, output). Decided during roadmap review 2026-06-18: this is redundant — people will read the SKILL.md.

Scope

• Remove README.md from skills where it just mirrors SKILL.md.
• The duplication exists because GitHub renders README.md (not SKILL.md) when browsing a folder.

Option to evaluate (not blocking)

• Symlink README.md -> SKILL.md per skill so GitHub still renders something on folder browse.
• Caveat: symlinks are fragile across OSes; must not produce an empty file. If it doesn't hold cleanly, drop the README entirely — it's a nice-to-have, not required.

QA

• No skill keeps a README that just restates its SKILL.md
• Folder browse on GitHub still shows useful high-level info (via symlink) OR README cleanly removed
• No empty/broken files left behind

[blafourcade]

Done. Shipped by #396 (refactor: remove per-skill README.md mirrors, retarget to SKILL.md), merged into next on 2026-07-07: 39 per-skill README.md removed, references retargeted. Reaches main at the next release.