[Issue #40] Fix CLI dependencies

[widal001]

Summary

Fixes how the path tsp CLI is resolved in the CommonGrants CLI, so that cg init and cg compile can serve as thin-wrappers for tsp init and tsp compile

• Relates to [CLI] Prepare @common-grants/cli for usability tests #40
• Time to review: [xx] minutes

Changes proposed

What was added, updated, or removed in this PR.

• Adds @typespec/compiler as a direct dependency
• Changes how we resolve the path to the tsp binary
• Adds back the default-api template

Context for reviewers

Testing instructions, background context, more in-depth details of the implementation, and anything else you'd like to call out or ask reviewers. Explain how the changes were verified.

1. Checkout the PR locally
2. Change directory into the cli/: cd cli
3. Run npm pack
4. In a separate clean directory install the tarball: npm install <path-to-tarball>
5. Run npx cg init