Route general sessions to preferred account

[cbusillo]

Summary

• route fresh CLI general sessions to the ChatGPT account whose weekly/secondary reset expires first
• keep proactive routing ChatGPT-only and avoid account movement for resumed/non-general sessions
• distinguish healthy future reset metadata from real limit blockers, and consume expired temporary limit retries correctly
• ignore generated root cache artifacts

Validation

• cargo test -p code-core account_switching --lib
• ./build-fast.sh