Register context as a sub-app of the actor Typer group so commands are
accessible under the canonical specification path `agents actor context`.
The top-level `agents context` group remains as a deprecated alias
(with Typer deprecated=True) for one release cycle.
Key changes:
- context.app registered under actor.app in main.py
- `rm` subcommand renamed to `remove`; `rm` kept as hidden deprecated
alias that prints a deprecation warning before delegating
- Programmatic rm_command() deprecated in favor of remove_command()
- Help text updated to reference canonical `agents actor context` paths
- Behave and Robot tests updated to use canonical paths and renamed
subcommand; assertion for context help lowercased for flexibility
- All nox sessions pass: lint, typecheck, unit_tests (495 features,
12731 scenarios), coverage at 97%
ISSUES CLOSED: #888
freemo