chore: add CLAUDE.md for Claude Code development guidance

[georgexu99]

CLAUDE.md should be shared repo-wide, though individual users can add their own user-level CLAUDE.md files to add individual preferences.

This will help our claudeguy be more efficient and accurate in its spelunking.

[MarshallOfSound]

I wouldn't leave this in your CLAUDE.md file, rather everything in this file should be addressed to Claude.

E.g.

This document helps Claude understand the Sleuth repo structure and common development patterns.

[MarshallOfSound]

Suggested change

	**Always use yarn instead of npm** - this project enforces yarn usage.
	IMPORTANT: Never attempt to run `npm`, instead always run the equivalent `yarn` command

"IMPORTANT:" is some magic to make claude pay more attention, bold doesn't have the same effect in aggregate

[MarshallOfSound]

I'd add a note here that claude should avoid running these commands as they are slow, instead prefer running test, tsc or lint to validate changes rapidly. Other you might find claude running yarn package after every file edit in rare cases.

[MarshallOfSound]

Two easy notes that are pretty generically helpful:

IMPORTANT: never disable a lint rule or add @ts-ignore unless explicitly asked to do so by the user.
If you are unable to solve a problem without disabling a lint rule, stop and ask the user for
guidance first.

**CRITICAL: NEVER use --no-verify flag with git commands.** This bypasses pre-commit hooks that enforce code quality and can introduce broken code into the repository. Always fix the underlying issues that cause hooks to fail instead of bypassing them. If a hook is failing, address the specific linting, formatting, or test failures it identifies.