Refine coding standards and testing guidelines

- Updated coding rule descriptions for clarity and emphasis on readability, meaningful comments, and test verification.
- Adjusted thresholds for test coverage on business logic from 80% to 75%, aligning with the canonical reference in `cursor-meta.mdc`.
- Enhanced guidelines for handling skipped tests, emphasizing the need for investigation and classification.
- Introduced completeness audit requirements for research decomposition to ensure thoroughness in addressing problem dimensions.

.cursor/rules/testing.mdc

@@ -8,7 +8,7 @@ globs: ["**/*test*", "**/*spec*", "**/*Test*", "**/tests/**", "**/test/**"]
 - One assertion per test when practical; name tests descriptively: `MethodName_Scenario_ExpectedResult`
 - Test boundary conditions, error paths, and happy paths
 - Use mocks only for external dependencies; prefer real implementations for internal code
-- Aim for 80%+ coverage on business logic; 100% on critical paths
+- Aim for 75%+ coverage on business logic; 100% on critical paths (code paths where a bug would cause data loss, security breaches, financial errors, or system outages — identify from acceptance criteria marked as must-have or from security_approach.md). The 75% threshold is canonical — see `cursor-meta.mdc` Quality Thresholds.
 - Integration tests use real database (Postgres testcontainers or dedicated test DB)
 - Never use Thread Sleep or fixed delays in tests; use polling or async waits
 - Keep test data factories/builders for reusable test setup