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/README.md

@@ -0,0 +1,40 @@
+# Examples
+
+This directory contains exemplar YAML files showing the full schema for each extension type.
+
+**These are reference examples, not actual entries.**
+
+## Usage
+
+When adding a new entry to `data/{category}/`, use the corresponding example as a reference:
+
+| Adding to... | Reference |
+|-------------|-----------|
+| `data/plugins/` | [plugin.yaml](plugin.yaml) |
+| `data/themes/` | [theme.yaml](theme.yaml) |
+| `data/agents/` | [agent.yaml](agent.yaml) |
+| `data/projects/` | [project.yaml](project.yaml) |
+| `data/resources/` | [resource.yaml](resource.yaml) |
+| `data/forks/` | [fork.yaml](fork.yaml) |
+
+## Required vs Optional Fields
+
+### Required (all entries must have)
+- `name` - Display name
+- `repo` - Repository URL (https://github.com/...)
+- `tagline` - Short description (max 120 chars)
+- `description` - Full description (can be multi-line)
+
+### Optional (include if relevant)
+- `scope` - Installation scope: `[global]`, `[project]`, or `[global, project]` (defaults to `[global]`)
+- `tags` - Array of strings for filtering
+- `min_version` - Minimum OpenCode version (semver)
+- `homepage` - Documentation URL if different from repo
+- `installation` - Markdown installation instructions
+
+## Notes
+
+- **Type is derived from directory** - No `type` field needed; it's inferred from the folder
+- **Scope is optional** - Defaults to `[global]`; add if project-level install is relevant
+- **Installation is markdown** - Use headers, code blocks, lists as needed
+- **Schema allows additional fields** - Future fields can be added without breaking existing entries