Optimize Context Builder ranking and token budget

[itsflaid]

Summary

• exclude tests, specs, and fixtures from normal product questions
• allow test context when an English query explicitly requests tests or fixtures
• apply conservative English scope boosts for CLI, web UI, and documentation
• cap English navigation queries at two files and 60 lines per file
• keep scope matching as a boost rather than a hard package exclusion
• document focused testing and measured context reduction

Impact

The measured where scanner prompt payload on the DevMap snapshot dropped from about 20,844 characters to 4,423 characters before tokenization, while the existing evaluation remains at 20/20 top-1 accuracy and 20/20 top-3 recall.

Verification

• pnpm --filter devmap test (53/53)
• pnpm build:cli
• pnpm test:package-e2e
• git diff --check

Closes #13