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/issue-discover/phases/03-discover-by-prompt.md

@@ -234,6 +234,7 @@ while (shouldContinue && iteration < maxIterations) {
 
   iterationPlan.dimensions.forEach(dimension => {
     const agentId = spawn_agent({
+      agent_type: "cli_explore_agent",
       message: buildDimensionPromptWithACE(dimension, iteration, cumulativeFindings, iterationAceResults, iterationDir)
     });
     dimensionAgents.push({ agentId, dimension });
@@ -413,12 +414,11 @@ function buildDimensionPromptWithACE(dimension, iteration, previousFindings, ace
   );
 
   return `
-## TASK ASSIGNMENT
+## TASK ASSIGNMENT (agent_type: cli_explore_agent)
 
 ### MANDATORY FIRST STEPS (Agent Execute)
-1. **Read role definition**: ~/.codex/agents/cli-explore-agent.md (MUST read first)
-2. Read: {projectRoot}/.workflow/project-tech.json
-3. Read: {projectRoot}/.workflow/specs/*.md
+1. Read: {projectRoot}/.workflow/project-tech.json
+2. Read: {projectRoot}/.workflow/specs/*.md
 
 ---