feat(codex): expanded slash command surface #34

Post-MVP follow-up to #13. Extends the codex slash dispatcher with the rest of the upstream slash command set beyond the MVP lifecycle five (/exit, /help, /clear, /compact, /restart).

Scope

Add codex's remaining ~40 built-in slash commands to the dispatch table. Source-of-truth: COMPATIBILITY.md ## Codex slash-commands section + research-codex-coverage skill.

Logical groups (split into multiple PRs if a single PR is too large):

• Config / model: /config, /model, /temperature, etc.
• Tool + file primitives: /files, /diff, etc.
• Logging / debugging: any /log, /debug analogs codex ships.
• Catch-all: anything left after the above.

Each row that flips updates COMPATIBILITY.md in the same PR.

Non-goals

• Approval + sandbox slash commands — see [approval/sandbox issue, separate].
• Adding behavior testagent can't model (e.g. real /diff against a real working tree). Accept-and-render is the right shape.
• Net-new slash commands testagent doesn't already have a dispatch pattern for.

Sequencing

After #13 MVP ships (which establishes the codex dispatcher).