feat: store and reuse CLI credentials

[Deivid00007]

Resolves #2

Summary

• store token, cert path, and cert key in the CLI config during configure
• allow client.New to reuse the stored endpoint when no endpoint is passed
• select TLS transport when the endpoint is secure or a client certificate pair is configured
• add bearer-token per-RPC credentials when a stored token is available
• add tests for TLS detection, certificate-pair validation, and token dial options

Test plan

go test ./...

Result:

ok github.com/Permify/permify-cli/core/client
ok github.com/Permify/permify-cli/core/config
all other packages: no test files

Notes

• The implementation rejects partial certificate configuration; cert path and cert key must be set together.
• Plain endpoints still use insecure transport unless TLS/cert configuration is present.
• Token auth is read from stored config and attached to gRPC dial options.