[codex] add workspace-based nota lookup

[upsetbit]

Summary

• replace the global config path flag with --workspace / -w
• resolve nfe emit mova to <workspace>/notas/mova.toml
• scaffold notas/example.toml from nfe init
• update README and CLI tests for the workspace flow

Validation

• go test ./...
• go test ./... -race -coverprofile=coverage.out
• go vet ./...
• go mod tidy && git diff --exit-code go.mod go.sum