Add `keep-coding-instructions: true` to all skill frontmatters please.

[heydylanwang]

When a superpowers skill is invoked, Claude Code replaces the active
coding instructions with the skill's prompt. This discards any rules
defined in the user's CLAUDE.md (coding style, comment language,
security constraints, etc.).

Claude Code 2.1.94 introduced the keep-coding-instructions frontmatter
field specifically to prevent this. Adding it to a skill preserves the
user's CLAUDE.md alongside the skill prompt instead of replacing it.

Request: Add keep-coding-instructions: true to the frontmatter of
all skills in this repo, e.g.:

---

name: brainstorming
keep-coding-instructions: true

This is a one-line change per skill file and would ensure superpowers
works correctly with user-defined project conventions without silently
overriding them.