feat(generate): implement `generate()` that orchestrates parse, map, render and metadata write

[thopatevijay]

• Implement packages/cli/src/generate.ts using previously created parser/mapper/renderer.

• Write metadata to out/.castui/metadata.json.

• Implement logging and progress (spinner).

• Add --no-install behavior.

Acceptance criteria

• Running node bin/castui.js --idl tests/fixtures/simple_idl.json --out ./tmp-out produces ./tmp-out with generated files and .castui/metadata.json.

• The CLI exits 0 on success; error codes on failure.

• tmp-out contains instruction pages matching the sample IDL.