Introduces dynamic completion inference for Cobra-based CLIs using the
hidden `__complete` subcommand. Iris can now automatically suggest
subcommands and flags for commands without hand-written specs.
Completions are structured, cached by binary modification time
(`mtime`), and safely isolated from hand-written specs.
Try testing with un-specced commands:
- `gh repo ` (suggests `clone`, `fork`, `sync`...)
- `kubectl get ` (suggests `pods`, `nodes`, `configmaps`...)
- `golangci-lint ` (suggests `run`, `fmt`, `linters`...)
