docs: add common testing gotchas

[bpamiri]

Summary

• Add "Common Gotchas" section to docs/src/working-with-wheels/testing-your-application.md covering 5 pitfalls discovered during Phase 1 feature testing
• Update CLAUDE.md testing section with accurate paths and key warnings
• Create .ai/wheels/testing/unit-testing.md AI reference doc for TestBox test infrastructure

Gotchas Documented

1. CFML closure scoping — closures can't access outer local vars; use shared structs
2. Model cache reload — &reload=true needed after adding new model CFCs
3. DROP+CREATE vs IF NOT EXISTS — stale tables miss schema changes in populate.cfm
4. Test model table naming — always call table() to avoid convention surprises
5. TestBox JSON parsing — non-standard booleans break strict parsers; use Node.js

Test plan

• No code changes, documentation only
• Verified all gotchas against live test environment

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