[plan] Add test coverage for expires field validation

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Objective

Add comprehensive test cases to ensure the expires field correctly validates against the schema and runtime implementation.

Context

Currently there may be insufficient test coverage for the expires field validation. We need tests that verify both schema validation and runtime parsing work consistently.

Approach

1. Identify existing test files for config_helpers.go (likely pkg/workflow/config_helpers_test.go)
2. Add test cases for parseRelativeTimeSpec() function:
   • Valid cases: "7d", "2w", "1m", "1y", "30D", "12M"
   • Invalid cases: "20h", "5H" (should return 0 and log error)
   • Edge cases: "0d", invalid format, empty string
3. Consider adding schema validation tests if not already covered
4. Verify tests pass with the updated schema

Files to Modify

• pkg/workflow/config_helpers_test.go (or create if doesn't exist)
• Possibly pkg/parser/schema_test.go or similar

Acceptance Criteria

• Test cases cover all valid time units (d, w, m, y)
• Test cases verify hour units are rejected
• Test cases verify the function returns 0 for invalid input
• Tests verify logging occurs for invalid units
• All tests pass with make test-unit
  Related to [plan] Fix expires field schema-implementation mismatch #7198

AI generated by Plan Command for discussion #7174