Publish npm package and add npx thinktank support

[that-github-user]

Summary

Currently installation requires git clone + npm link. Publishing to npm would enable:
```bash
npx thinktank run "fix the bug" -n 3
```
The release workflow (#28) is already in place. Need to:

1. Verify package.json metadata (author, repository, homepage)
2. Set up NPM_TOKEN secret in GitHub
3. Tag v0.1.0 and push to trigger release
4. Update README install instructions

[that-github-user]

Priority elevated. Publishing to npm is now the fix for the self-referential dogfooding bug (#136). When thinktank is installed globally, agents in worktrees interact with the code but the tool runs from the global install — cleanly separating infrastructure from codebase.

This is the single highest-impact improvement for reliable dogfooding.

[that-github-user]

Fixed in #146. Package name: thinktank-ai. Install: npm install -g thinktank-ai. Binary: thinktank. To publish: add NPM_TOKEN secret, tag v0.1.0, push tags. Also resolves the dogfooding worktree bug (#136) — global install separates tool from codebase.