docs(skills): clarify env example requirements

[TheRealAgentK]

Summary

• Clarifies that integration-test env vars must be added to root .env.example in the same PR
• Calls out optional test IDs and destructive-test-only variables as part of the setup contract
• Updates review/build/SDK-upgrade skills to treat missing .env.example entries as blocking for PRs that add or change integration tests
• Adds focused grep cross-check commands for authors and reviewers
• Caps the test extra to aiohttp<3.14 because aioresponses 0.7.8 cannot construct aiohttp 3.14.x ClientResponse objects yet

Validation

• git diff --check
• python -m pytest tests/ -v --tb=short --cov=autohive_integrations_sdk --cov-report=term-missing --cov-report=xml:coverage.xml — 75 passed

[github-actions]

Coverage — d4e8dff (test: cap aiohttp for aioresponses compatibility) by @TheRealAgentK

Total coverage: 100%

File	Stmts	Miss	Cover	Missing
src/autohive_integrations_sdk/__init__.py	2	0	100%
src/autohive_integrations_sdk/integration.py	358	0	100%