Probe Codex permission denial and observer recovery

[minglong51]

The Phase 0 qualifier can now exercise a pending Codex permission approval with --scenario permissions. It requests network permission, verifies observer restart and fresh-source recovery while the provider stays alive, then sends an empty turn-scoped grant and requires source resolution. Input remains the default scenario; results remain unqualified and the capability matrix stays experimental.

Validation: all 122 existing tests passed unchanged. The isolated permission probe passed with 45 messages and four source reads; the input probe passed with 41 messages and three source reads. Both private journals matched their captures, no execution items appeared in the permission capture, and copied credentials were removed. Malformed permissions, remote environments, other approval methods, and execution items were rejected in focused checks; provider_evidence.py --check passed.