feat(schema): refine and expand extension metadata schema

- Introduce `scope`, `tags`, `min_version`, `homepage`, and `installation` fields for enhanced discoverability and guidance.
- Remove `install` and `compatibility` objects, replacing them with a simplified `installation` string field.
- Add `examples/` directory with full exemplar files for each extension type.
- Update `schema-design.md` to reflect new schema, clarify field definitions, and improve documentation structure.

examples/fork.yaml

@@ -0,0 +1,89 @@
+# Example Fork Entry
+# Forks are modified builds of OpenCode with custom features or patches.
+# Place actual entries in: data/forks/your-fork-name.yaml
+
+# ============================================================================
+# REQUIRED FIELDS
+# ============================================================================
+
+name: Example Enterprise Fork
+repo: https://github.com/example/opencode-enterprise
+tagline: OpenCode fork with enterprise authentication and audit logging
+description: |
+  A fork of OpenCode designed for enterprise environments.
+  
+  Additions:
+  - SAML/SSO authentication
+  - Audit logging for compliance
+  - Custom model routing
+  - Air-gapped deployment support
+
+# ============================================================================
+# OPTIONAL FIELDS
+# ============================================================================
+
+# Note: Forks don't use 'scope' - they replace the entire OpenCode installation
+
+tags:
+  - enterprise
+  - fork
+  - authentication
+  - audit
+
+min_version: "1.0.0"
+
+homepage: https://example.com/opencode-enterprise
+
+installation: |
+  ## Prerequisites
+  - Go 1.21+ (for building from source)
+  - Or: Docker (for containerized deployment)
+
+  ## Installation from Source
+  ```bash
+  # Clone the fork
+  git clone https://github.com/example/opencode-enterprise
+  cd opencode-enterprise
+
+  # Build
+  go build -o opencode-enterprise ./cmd/opencode
+
+  # Install (replaces standard opencode)
+  sudo mv opencode-enterprise /usr/local/bin/opencode
+  ```
+
+  ## Docker Installation
+  ```bash
+  docker pull example/opencode-enterprise:latest
+  alias opencode='docker run -it --rm \
+    -v ~/.config/opencode:/root/.config/opencode \
+    -v $(pwd):/workspace \
+    example/opencode-enterprise'
+  ```
+
+  ## Configuration
+  Enterprise-specific configuration in `opencode.json`:
+  ```json
+  {
+    "enterprise": {
+      "sso": {
+        "provider": "okta",
+        "domain": "company.okta.com"
+      },
+      "audit": {
+        "enabled": true,
+        "destination": "s3://audit-logs/"
+      }
+    }
+  }
+  ```
+
+  ## Files Modified
+  - `/usr/local/bin/opencode` (replaced binary)
+  - `~/.config/opencode/opencode.json` (enterprise config)
+
+  ## Reverting to Standard OpenCode
+  ```bash
+  # Reinstall standard OpenCode
+  curl -fsSL https://opencode.ai/install | bash
+  ```