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.

.opencode/config/project.md

@@ -0,0 +1,40 @@
+# OpenCode Project Configuration
+
+## Project Info
+
+- **Name:** AI Coding Starter Kit - Opencode - PHP Edition
+- **Repository:** https://git.shadow-land.de/madgerm/ai-coding-starter-kit-opencode
+- **Description:** PHP project template with AI-powered development workflow optimized for OpenCode. SQLite-first dev, MariaDB/PostgreSQL production.
+
+## Skills
+
+The following skills are available in `.opencode/skills/`:
+
+| Skill | Description |
+|-------|-------------|
+| `requirements` | Creates feature specs with user stories, AC, edge cases |
+| `architecture` | Designs tech architecture (class structure, DB schema) |
+| `php` | Builds PHP code, migrations, and tests |
+| `qa` | Tests features against acceptance criteria |
+| `docs` | Documents API endpoints and maintains wiki structure |
+| `deploy` | Deploys to traditional hosting (LAMP, Docker, bare metal) |
+
+## Agents
+
+Heavy tasks (implementation, QA) run as forked agents with isolated contexts.
+
+## Rules
+
+Auto-applied coding standards in `.opencode/rules/`:
+- `general.md` - Git workflow, feature tracking
+- `php.md` - PHP code standards, portable SQL
+- `database.md` - SQLite/MariaDB/PostgreSQL portability
+- `security.md` - Secrets, headers, auth
+
+## Default Branch
+
+`main`
+
+## Feature ID Pattern
+
+`PROJ-1`, `PROJ-2`, etc. (sequential)