Add --required and --informational as mutually exclusive boolean options
to the `agents validation add` CLI command. When specified, they override
the `mode` field from the YAML config file. This aligns the CLI with the
specification (specification.md line 22339) which states the validation
mode can be set "via --required/--informational on agents validation add".
The fix resolves the spec contradiction by:
- Implementing the flags in the CLI (per Core Concepts > Validation Mode)
- Updating the formal CLI reference to include the new flags
- Adding an exception to Design Principle #3 for validation add
- Removing the spurious positional name argument from the walkthrough
TDD tests from #1102 now run normally with @tdd_expected_fail removed.
New edge-case tests cover mutual exclusivity (both flags rejected).
Also excludes tool/wrapping.py from semgrep exec/compile rules since
that module intentionally uses exec() in a controlled sandbox for the
validation transform feature.
ISSUES CLOSED: #1038
brent.edwards