fix(init): refresh Codex hooks with hooks-only

[blankanswer]

Summary

• Extend gortex init --hooks-only so it refreshes Codex hooks in ~/.codex/config.toml alongside Claude Code hooks.
• Keep hooks-only scoped to hook surfaces only: no MCP rewrite, no AGENTS.md, no skills/indexing, no project marker, and no global config update.
• Respect --agents / --agents-skip in hooks-only mode, matching normal init selection semantics.
• Document --hooks-only as refreshing supported agent hooks.

Changes

• Added codex.InstallHooksOnly(...), which reuses existing Codex hook upsert logic while touching only top-level hooks.
• Refactored Codex normal init to share the same hook upsert helper.
• Updated runInitHooksOnly to:
  • refresh Claude Code hooks when claude-code is selected;
  • detect and refresh Codex hooks when codex is selected;
  • skip Codex when filtered out by --agents or --agents-skip.
• Added integration coverage for hooks-only allow-list / skip behavior.
• Added Codex adapter tests for fresh install, idempotency, preserve user hooks, preserve MCP/unrelated keys, force replacement, and dry-run behavior.

Out of scope

• Normal gortex init behavior changes.
• Codex hook semantics changes.
• Codex PostToolUse source-read or file-list enrichment.
• MCP tool-name hooks.
• apply_patch hooks.
• resolver, indexer, daemon, graph, or MCP tool changes.

Tests

• go test ./cmd/gortex
• go test ./internal/agents/codex
• go test ./internal/agents/claudecode
• git diff --check