feat(claude): consolidate simplify-code into simplify skill (#1934)

The built-in `simplify` skill is compiled into the CLI and can't be edited
directly, so rename the project's `simplify-code` skill to `simplify` to
shadow it for this repo, folding in its diff-scoped, quality-only workflow
and grounding the guidance in Compass's actual paths, aliases, Zustand store
pattern, and bun/biome commands.

Co-authored-by: Claude Sonnet 5 <noreply@anthropic.com>

Author: tyler-dane