Closed vocabulary of effort labels across all supported providers.
Typing the per-provider tuples with this alias catches typos in the vocabulary
at check time. It does not express the deeper invariant that a label must be
supported by a specific model — that is enforced at runtime by
supported_efforts_for_model.
This vocabulary is also hand-duplicated as display text in the /effort
argument_hint (command_registry.py) and in COMMANDS.md; those are not
type-checked against this alias, so update them in lockstep when it changes.
