Use crypto.randomUUID() for worktree branch names to prevent collisions

[that-github-user]

Summary

src/utils/git.ts:22:

const branchName = \`thinktank/agent-\${id}-\${Date.now()}\`;

Uses Date.now() for uniqueness. If two thinktank processes start in the same millisecond, branch names could collide.

Proposed fix

const branchName = \`thinktank/agent-\${id}-\${crypto.randomUUID().slice(0, 8)}\`;

Low priority but easy fix.

[that-github-user]

Fixed in #41 (combined with #25). Worktree branch names now use crypto.randomUUID() instead of Date.now() to prevent collisions when running multiple thinktank processes simultaneously.