fix: raise a clear RuntimeError when action_scope runs outside @inject

[lesnik512]

Problem

Calling action_scope(ctx) from a command that is not decorated with @inject failed inside the ctx.meta lookup with an error that names a private key and nothing the user can act on:

KeyError: 'modern_di_typer.command_container'

Verified empirically with CliRunner before the change.

Change

action_scope catches KeyError on the ctx.meta[_COMMAND_CONTAINER_KEY] lookup only and raises:

RuntimeError: No modern-di command container found for this command. Decorate the command with @inject so action_scope has a per-command container to nest under.

with from None, so the traceback ends at the actionable message. Behaviour inside an @inject command is unchanged. The README action_scope bullet notes the new error.

This completes the sweep started by #47, following the guide rule in modern-python/modern-di#490: a plain package-local RuntimeError, not a ModernDIError subclass.

Tests

Written red first in tests/test_commands.py:

• test_action_scope_without_inject_raises_clear_error: Typer app with setup_di, command without @inject that opens action_scope(ctx); failed with the original KeyError: 'modern_di_typer.command_container' before the fix

Asserts RuntimeError matching @inject. just lint and just test-ci pass at 100% coverage.