Add real tests for packages/cli (current test script is a smoke print)

[Railly]

Context

packages/cli/package.json defines "test": "node dist/cli.js --help". That verifies the binary boots but asserts nothing about theme generation output.

Task

Add unit or integration tests around the CLI's core flows: generating a theme, compiling providers, and error handling for invalid input.

Acceptance criteria

• bun test in packages/cli runs real assertions
• At least one test validates generated output shape for one provider
• CI-friendly (no network needed)

[Railly]

Partial progress via #71: build/lint/from now ship with 20 real bun tests (fixtures include real extraction data). Remaining scope for this issue: cover the installer flows (quick/list/cleanup) and point the package test script at bun test instead of the --help smoke print.