Add solitary/sociable/integration test levels to agent prompts and quality gate

[hiroshinishio]

Summary

• Introduce 3 test levels (solitary/sociable/integration) in agent prompts, replacing the old "unit test only" bias
• Add integration test quality gate (db_operations_use_real_test_db, api_calls_tested_end_to_end, env_var_guards_for_secrets) to checklist
• Add env var guard patterns: free services skip locally but run in CI, paid APIs always skip but tests exist as documentation
• Remove duplicated rules from pr.xml (now single source of truth in coding_standards.xml)
• Update PR titles from "Add unit tests" to "Add unit and integration tests"
• Prefer npm "test" script over "test:unit" so integration tests (with env var guards) are included

Social Media Post (GitAuto)

Upgrade test generation to produce solitary, sociable, and integration tests

• Agent now writes tests at 3 levels instead of only mocked unit tests
• Integration tests use real test infrastructure when available
• Env var guards let integration tests skip locally, run in CI where secrets exist
• New quality gate catches missing integration tests during automated reviews

Social Media Post (Wes)

Customer told us they wanted more integration tests from our agent. Checked the PRs. Every single one was pure mocks, even when their repo had test DB helpers sitting right there. The prompt said "use test infrastructure if available" but the model ignored it every time. Why? One buried line loses against the rest of the prompt biasing toward mocks. Prompt alone is not enough. Added a quality gate that programmatically flags missing integration tests.