feat(probe): add agent_financial probe and detector for OWASP LLM06

[praveshuma]

Why

Fills a gap in OWASP LLM06 (Excessive Agency) and OWASP LLM01 (Indirect Prompt Injection) for payment and financial agent setups.

Summary

• Added agent_financial probe module (UnauthorizedPaymentExecution, FinancialToolBypass).
• Added PaymentInvocation detector for payment function signatures and JSON payloads.
• Includes unit tests and Sphinx documentation.

##Testing

• Unit Tests: "python -m pytest tests/probes/test_agent_financial.py tests/detectors/test_agent_financial.py" — 3/3 passed in 0.36s (100% pass rate).

##End-to-end scanner execution:

• Executed local scan using " python -m garak --target_type test --target_name Blank --probes agent_financial " — 45/45 attempts completed successfully.
• Formatting: Verified and formatted with "black".
  Results - Successfully instantiated generator, queued both probes, executed all attempts against detector, and generated JSON/HTML reports without errors.

All code was also formatted according to project standards using black*******

AI Usage: AI assistance was used to draft initial probe/detector code boilerplates, unit test cases, and Sphinx RST documentation. All code was manually reviewed, integrated, formatted with black, and verified by running pytest locally.