Refresh credentialed routes during session

[winston-openai]

Summary

• store credentialed routes behind session-scoped runtime state
• refetch routes before new turns and after runtime config refreshes
• rebuild managed proxy hooks only when the credentialed route set changes

Validation

• just fmt
• cargo test -p codex-core (blocked by existing untouched turn_extension_data errors in core/src/tasks/mod.rs)
• just fix -p codex-core (blocked by the same existing turn_extension_data errors)

[github-actions]

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