docs(codex): document hook coverage closeout

[blankanswer]

Summary

Documents the completed Codex hook integration coverage and closes #206.

Codex now has:

• SessionStart orientation for startup|resume|clear|compact
• Bash PreToolUse soft graph guidance
• Gortex MCP read-tool PreToolUse compress-bodies guidance
• Bash PostToolUse graph enrichment for grep/read/list-shaped output
• gortex init --hooks-only refresh support for Codex hooks

Lifecycle rationale

This intentionally does not add separate PreCompact, PostCompact, or Stop hooks.

SessionStart already covers the compact source, which is the safer orientation path for Codex. Stop has continuation semantics and should remain a separate, explicit feature if needed.

Out of scope

• PreCompact / PostCompact runtime behavior
• Stop continuation behavior
• SubagentStart / SubagentStop
• apply_patch
• deny / enforcement behavior
• input rewriting or updatedInput
• output suppression
• Claude / Gemini / Antigravity behavior changes

Tests

• git diff --check

Not run: docs-only change.

Closes #206.