Support Codex hook registration

[urugus]

Bug

Codex CLI hook registration needs a different config file and event set than Claude Code. The current hook installer only writes Claude Code hooks, while Codex users need entries in ~/.codex/hooks.json.

Codex stable also does not support async hooks yet. If Codex hooks are registered with "async": true, Codex prints:

skipping async hook in ~/.codex/hooks.json: async hooks are not supported yet

and skips the hook.

Fix

Register zellaude hooks for both agents when their config directories exist:

• Claude Code: ~/.claude/settings.json
• Codex CLI: ~/.codex/hooks.json

The hook command now receives an agent argument (claude or codex) so the plugin can distinguish sessions and render Codex with distinct symbols. Claude hook entries keep "async": true; Codex hook entries omit it until Codex supports async hooks.

The cleanup logic also removes older no-argument Claude hook entries to avoid duplicates during upgrades.

Verification

• cargo fmt --check
• git diff --check
• cargo check --target aarch64-apple-darwin
• Temp HOME hook install smoke test:
  • Claude entry is installed as zellaude-hook.sh claude with "async": true
  • Codex entry is installed as zellaude-hook.sh codex without "async"
  • Older no-argument Claude hook entries are removed
• cargo build --release --target wasm32-wasip1 could not complete in this local environment because the active Homebrew Rust toolchain could not find the wasm32-wasip1 core crate, even after rustup target add wasm32-wasip1 reported the target as installed.