Support a short check syntax (check: no_token_in_logs)

[DataDave-Dev]

Context

Built-in checks are referenced verbosely:
check: "python3 -m becwright.checks.no_token_in_logs". That leaks the Python
implementation and confuses people watching non-Python repos. A short form like
check: no_token_in_logs would be much friendlier.

Proposed approach

• When a rule's check value is a bare built-in name (it matches a module in
  becwright.checks), expand it to the real invocation before running.
• Keep the full shell-command form working (fully backward compatible).
• Decide where resolution happens (likely when loading rules in rules.py, or
  just before running in engine.py).

Acceptance criteria

• check: no_token_in_logs runs the corresponding built-in check.
• The existing full-command form still works.
• Tests cover both forms.

Notes

This changes how the check field is interpreted — please discuss the exact
resolution rules (e.g. how args like forbid --pattern ... fit) in this issue
before implementing.

Relevant files

src/becwright/rules.py, src/becwright/engine.py.