fix(cli): align install and v2 dev workflows

[bolodissenoura]

Summary

• Fixes Go installation by using the canonical module path and adding cmd/abacatepay so Go users can install the expected abacatepay binary.
• Narrows the CLI to the requested supported surface: auth, webhook listening, and dev-mode payment simulation.
• Updates payment simulation to API v2: POST /v2/transparents/simulate-payment?id=<charge-id>.
• Removes unsupported commands/features from the current codebase until there is documented API v2 parity.
• Updates README installation and usage docs.

Closes #32.

Validation

• go mod tidy
• go test ./...
• go build ./...
• GOBIN=/tmp/abacatepay-cli-bin go install . and root CLI help smoke test
• GOBIN=/tmp/abacatepay-bin go install ./cmd/abacatepay and abacatepay help smoke test

Notes

The --local flag is kept as a backwards-compatible no-op because API v2 uses the same public endpoint for production and dev mode; the API key determines the environment.

The old root Go install path still works and produces abacatepay-cli; the documented Go path now installs abacatepay.