refactor(codex): drop the .codex/agents sidecar; rely on nested skill agents (#173)

Codex auto-discovers subagents bundled inside an installed skill's own
agents/ folder, so the separate .codex/agents/*.toml sidecar was redundant.

- cli: remove installCodexAgents/isCodexLikely and their install/update calls
- context.mjs: remove the CODEX_AGENT_MISSING self-heal directive
- build: drop codex agentFormat so no top-level .codex/agents is emitted; the
  nested in-skill .toml bundling is the whole delivery
- remove the tracked .codex/agents/*.toml and the gitignore exception
- docs + build.test.js updated for the nested layout
- CLI patch version bump; skill version unchanged

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

package.json

@@ -1,6 +1,6 @@
 {
   "name": "impeccable",
-  "version": "2.3.0",
+  "version": "2.3.1",
   "author": "Paul Bakaus",
   "description": "Design skills, commands, and anti-pattern detection for AI coding agents",
   "keywords": [