.sf/skills/ is the project-local skill override directory. This override
inherits all sf-wiki defaults and adds one project-specific rule: wiki
pages use UPPERCASE filenames (INDEX.md, ARCHITECTURE.md, etc.) to match
the .sf/ operational file convention (DECISIONS.md, KNOWLEDGE.md, etc.).
The built-in src/resources/skills/sf-wiki/SKILL.md stays generic (lowercase).
Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>