Unify OpenCode and Codex starter kits

- Add .shared/prompts/ with tool-neutral prompts
- Add .opencode/config/project.md, rules/, skills/ from opencode-kit
- Add .codex/config/project.md from codex-kit
- Copy .shared/prompts/ to both .opencode/prompts/ and .codex/prompts/
- Add features/INDEX.md and features/README.md
- Update README with unified structure

The two original starter kits are now redundant.

.codex/prompts/deploy.md

@@ -0,0 +1,27 @@
+# Deploy Prompt Template
+
+Use this prompt structure for deployment:
+
+```
+Read the feature spec at features/PROJ-X-feature-name.md.
+Deploy the implemented feature to production.
+
+Steps:
+1. Run build/lint/tests locally
+2. Create git tag: v1.0.0-PROJ-X
+3. Push to origin
+4. Trigger deployment pipeline
+5. Verify production URL works
+6. Update feature spec with deployment status:
+
+## Deployment
+**Status:** ✅ Deployed
+**Deployed:** YYYY-MM-DD
+**Production URL:** https://...
+**Git Tag:** v1.0.0-PROJ-X
+```
+
+Example:
+```
+<codex|opencode> exec "Deploy PROJ-1-login: run npm build, create tag v1.0.0-PROJ-1, push. Verify at https://www.example.com. Update feature spec."
+```