feat: convert all codex agent definitions from .md to .toml format

Convert 20 agent .md files to Codex-native .toml format with proper
metadata (name, description, model, sandbox_mode, developer_instructions).
Update all 19 skill files to use agent_type references instead of .md
file paths. Remove "Read role definition" bootstrapping step from spawn
messages since TOML developer_instructions replaces it.

Agent format: YAML frontmatter + body → TOML with inline instructions
Calling schema: agent: "path.md" → agent_type: "toml_name"
Sandbox: read-only for exploration agents, workspace-write for executors

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

.codex/skills/clean/SKILL.md

@@ -159,12 +159,12 @@ let exploreAgent = null
 try {
   // Launch cli-explore-agent
   exploreAgent = spawn_agent({
+    agent_type: "cli_explore_agent",
     message: `
 ## TASK ASSIGNMENT
 
 ### MANDATORY FIRST STEPS
-1. Read: ~/.codex/agents/cli-explore-agent.md
-2. Read: ${projectRoot}/.workflow/project-tech.json (if exists)
+1. Read: ${projectRoot}/.workflow/project-tech.json (if exists)
 
 ## Task Objective
 Discover stale artifacts for cleanup.