[Agentic] Add MAX_RETRY_ATTEMPTS constant to payment service config (#174)

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Summary

Automated implementation of #174: Add MAX_RETRY_ATTEMPTS constant to payment service config

This PR was created by the agentic coding pipeline. The code was written by Claude Code and reviewed by the multi-model agentic review loop (Claude + Gemini).

Review Summary

• Verdict: ACCEPTED
• Rounds: 3

Findings for Human Review

5 finding(s) from the final review were triaged automatically (0 high, 4 medium). Please review before approving.

MEDIUM (4)

• MAX_RETRY_ATTEMPTS lacks validation constraints (src/payments/config.py:19)
  The MAX_RETRY_ATTEMPTS constant is defined without any validation constraints. While not directly financial, this operational parameter could cause system instability if set to extreme values (e.g., 0
  Suggestion: Add validation similar to _validate_timeout() to ensure MAX_RETRY_ATTEMPTS is within reasonable bounds (e.g., 1-10). Consider making it configurable through environment variables with validation.
• Missing pytest marker for unit test file (tests/unit/test_compliance_gate.py:427)
  The test file tests/unit/test_compliance_gate.py is missing the required pytest marker. According to testing standards, every test file must include 'pytestmark = pytest.mark.unit' for unit tests or '
  Suggestion: Add 'pytestmark = pytest.mark.unit' at the top of the file after imports
• Missing pytest marker for unit test file (tests/unit/test_retry_agents.py:192)
  The test file tests/unit/test_retry_agents.py is missing the required pytest marker. According to testing standards, every test file must include 'pytestmark = pytest.mark.unit' for unit tests or 'pyt
  Suggestion: Add 'pytestmark = pytest.mark.unit' at the top of the file after imports
• Hardcoded operational constant MAX_RETRY_ATTEMPTS (src/payments/config.py:19)
  The MAX_RETRY_ATTEMPTS constant is hardcoded to 3 in src/payments/config.py. Operational parameters like retry attempts are often environment-specific and need to be configurable (e.g., differen
  Suggestion: Externalize MAX_RETRY_ATTEMPTS to be configurable via an environment variable, with a sensible default. For example, use int(os.getenv('PAYMENT_MAX_RETRY_ATTEMPTS', '3')) after importing os.

LOW (1)

• Test constant introduced without consistent application (tests/unit/test_compliance_gate.py:430)
  A test constant _TEST_API_KEY was introduced to replace hardcoded string values, but this pattern is not applied consistently throughout the test file. The constant is only used in two places while
  Suggestion: Either apply the constant pattern consistently to all similar hardcoded test values in the file, or consider if this single constant addition provides sufficient value. Review other test files for sim

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Created by the agentic SDLC pipeline. Human review is recommended before merge.

Closes #174