feat(codex): route shell commands through plugin hooks

[AZ-LL]

Add Codex plugin integration

Target branch: upstream develop

Summary

• Replaces Codex's default loose RTK.md plus AGENTS.md setup with a packaged RTK Codex plugin.
• Adds plugin-owned RTK Codex files: .codex-plugin/plugin.json, skills/rtk/SKILL.md, and hooks/hooks.json.
• Adds native rtk hook codex handling for Codex PreToolUse Bash payloads.
• Updates rtk init --codex, rtk init -g --codex, rtk init --codex --show, and rtk init --codex --uninstall to manage the plugin lifecycle.
• Keeps the implementation self-contained on upstream develop.

Behavior

• The plugin manifest advertises RTK command rewriting, points Codex to bundled skills, and registers plugin hook lifecycle config.
• The bundled RTK skill explains when to use RTK, automatic Bash rewriting, opt-out behavior, and validation with rtk gain.
• The Codex PreToolUse hook rewrites supported Bash commands such as git status to rtk git status.
• The hook config delegates directly to the native RTK hook processor with rtk hook codex on Linux/macOS and rtk.exe hook codex through commandWindows on native Windows.
• RTK_EXE can be set before rtk init --codex to write an explicit executable path into the installed hook config.
• The hook still matches Codex Bash tool payloads; the matcher name does not imply that native Windows needs a Unix shell launcher.
• rtk hook codex ignores empty input, malformed JSON, non-Bash tools, missing commands, unsupported commands, already-RTK commands, and heredocs.

Safety

• The Codex hook delegates command selection to RTK's existing rewrite registry and heredoc guard instead of adding new command filters.
• Rewrites emit Codex-supported permissionDecision: "allow" with updatedInput.command; RTK does not emit unsupported permissionDecision: "ask" rewrites.
• Hook runtime processing failures do not block the original Codex tool call.
• Uninstall removes only RTK-managed plugin state, marketplace entries, and legacy RTK-managed Codex guidance.
• Legacy cleanup preserves unmanaged user-owned RTK.md content and its AGENTS.md reference.

Validation

• cargo test codex: 26 passed, 0 failed.
• cargo fmt --all -- --check: pass.
• cargo build: pass.
• Native hook processor success path: returned an allow rewrite to rtk git status.
• Hook config tests cover direct Linux/macOS command generation, native Windows commandWindows, and install-time RTK_EXE override rendering.
• cargo clippy --all-targets: pass.
• cargo test --all: 1945 passed, 0 failed, 6 ignored.
• git diff --check: pass.

[CLAassistant]

All committers have signed the CLA.