Move and tweak SKILLS, so they're found and used

[Eddy Ashton (eddyashton)]

[Write a witty PR description outlining the following story:

• I kept getting annoyed by agents calling ctest, seeing it fail, and wasting time debugging venv activation issues.
• We already have a skill that tells them to use tests.sh.
• Finally asked the robot, and it explained that the skill was in the wrong place and the wrong format.

Include some gifs from Taken ("I have a particular set of skills"), and the Matrix (Neo getting skills injected, "I know kung fu") for visual learners. Maybe include screenshots of the VSCode /skills window before and after, to make it dead clear they were previously invisible but now auto-discovered. But I guess a cropped screenshot like that is beyond your abilities. Once upon a time I would have written this myself. Is this getting too meta?]

[Copilot]

Pull request overview

This PR adjusts the repository’s Copilot skill definitions and references so the existing “testing” and “formatting-and-linting” guidance is more likely to be discovered/used by agents (helping avoid wasted time running ctest directly instead of the project’s tests.sh wrapper).

Changes:

• Normalizes skill front matter (skill name values now match directory names; updated descriptions).
• Updates .github/copilot-instructions.md to link directly to the skill files.
• Minor wording tweak in the formatting/linting skill text.

Custom instructions used:

• .github/copilot-instructions.md

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
.github/skills/testing/SKILL.md	Updates skill front matter (name/metadata) and clarifies when to use the testing guidance.
.github/skills/formatting-and-linting/SKILL.md	Updates skill front matter and minor wording tweak in instructions.
.github/copilot-instructions.md	Fixes pointers to the new skill file locations so agents can find the intended guidance.

Suppressed comments (2)

.github/skills/testing/SKILL.md:4

• user-invocable is introduced in the skill front matter, but this key is not referenced anywhere else in this repo (and the skill itself doesn't explain what it does). To avoid future confusion, either add a brief note/link to the spec that defines this field, or remove it if it's not required.
  .github/skills/formatting-and-linting/SKILL.md:4
• user-invocable is added to the front matter, but it's not referenced anywhere else in this repository and isn't explained within the skill file. Consider documenting what it does (with a reference) or removing it if it's unnecessary, to keep the skill metadata self-explanatory.