refactor: Migrate from Claude Code to Codex CLI - .claude to .codex restructure

- Replaced .claude/ with .codex/ directory structure
- Created CODEX.md as root instructions for Codex
- Added .codex/prompts/ with templates for each development phase
- Added .codex/config/project.md for project configuration
- Removed .claude/agents/ (not compatible with Codex)
- Updated features/INDEX.md and docs/PRD.md references

.codex/prompts/deploy.md

@@ -0,0 +1,15 @@
+# Deploy Prompt Template
+
+Use this prompt structure with Codex:
+
+```
+Deploy to production:
+1. Run: npm run build (must succeed)
+2. Run: npm run lint (no errors)
+3. Run: vercel --prod
+4. Verify deployment URL
+5. Run smoke tests on production
+
+If build fails: fix errors first, then deploy.
+If lint errors: run npm run lint:fix, commit, then deploy.
+```