Add .claude/ to .gitignore

[scttbnsn]

.claude/ isn't in this repo's .gitignore, and .claude/worktrees/ already exists here as an empty directory. That combination is a live fuse rather than a theoretical one.

Without the ignore entry, all of these are demonstrated behaviour, not guesses:

• git add -A in the main checkout stages a nested worktree as an embedded gitlink — the broken-submodule shape — not as files. One careless git add -A while a worktree is populated puts it in history.
• rg --hidden walks into another agent's in-progress worktree and duplicates every match, including anything secrets-shaped. The ignore entry suppresses it, because ripgrep respects gitignore. find never does.
• git clean -fd and git stash -u skip a nested worktree, but git clean -ffd deletes it.

Fix is one line in .gitignore:

.claude/

I've appended it to this clone's .git/info/exclude as a local mitigation so nothing can fire today, but that's unshared and doesn't protect a second clone or another contributor. The committed line is the actual fix.

Shape file: standards/worktrees.md in codeswhat-ops, which also carries the rest of the worktree target state and this repo's measured drift.