feature: Codex support — detection, settings, parsed events, token and cost accounting

Feature Description

Codex support on the agent integration contract.

Proposed Solution

Same checklist as OpenCode support:

• Detect an installed Codex and locate its settings
• Patch it to use localhost:47600 and the Cortex CA; ask before editing, support revert
• Traffic parsed into typed events, not merely proxied
• Token counts and cost correct for its wire format
• Metrics aggregate alongside other agents
• A tool inventory, or state explicitly that tool pruning is unsupported
• Setup documented; verified depth stated

Additional Context

Part of the Cortex v0.9.0 release, stretch scope — deferred past v0.9.0 as the agent least
used internally, so it proves the least about the release. Depends on the agent integration contract.