v0.2.0 - Fix API compatibility and add comprehensive tests

Fix Homebrew formula name to 'mailtrap' instead of 'mailtrap-cli'

Allows: brew install mailtrap/cli/mailtrap

Rename homebrew tap from homebrew-tap to homebrew-cli

Install command is now: brew install mailtrap/cli/mailtrap

Rename inboxes to sandboxes in user-facing CLI commands

Align CLI terminology with the Mailtrap product UI which calls
them "sandboxes". The API paths remain as /inboxes internally
so no API changes are needed. When the API migrates, only the
internal URL paths need updating.

Changes:
- `mailtrap inboxes` → `mailtrap sandboxes`
- `--inbox-id` flag → `--sandbox-id` across messages, attachments,
  and sandbox-send commands
- Updated all docs, skills, evals, and tests