docs(routing): align Codex and Claude agent guidance

[MCamner]

Summary

Implements the canonical instruction slice of mq-hal v2.3.0 Phase 3.

• adds one shared MQ model-routing contract to the generated AGENTS.md surface
• keeps Claude equivalent by inheriting the same contract through @AGENTS.md
• requires inspect, cross-repo context, advisory-only shadow use, source/test verification, and escalation
• documents one Codex and one Claude Code VS Code workflow
• regenerates all nine checked-in examples

Verification

• export validation passed
• sensitive-content check passed
• token budget passed at 120/120 lines
• context links passed
• 55 unit tests passed (1 skipped)
• 9 repos x 2 entrypoints passed the canonical contract gate
• markdownlint passed

Scope

Canonical templates and examples only. Publishing generated entrypoints into each owner repo remains a separate rollout step.