Clean up schema by simplifying version structure (#379)

## Summary

Simplified the schema structure by:
- Replacing `version_detail.version` with direct `version` field  
- Removing unused `release_date` field from seed data
- Updating all API types, models, and tests to match new structure
- Maintaining backwards compatibility in API responses

This change makes the schema more intuitive and reduces nesting depth.

docs/guides/consuming/use-rest-api.md

@@ -34,9 +34,7 @@ You can also add custom metadata to servers using the `_meta` field. For example
   "name": "io.github.yourname/weather-server",
   "description": "MCP server for weather data access",
   "status": "active",
-  "version_detail": {
-    "version": "1.0.0"
-  },
+  "version": "1.0.0",
   "packages": [
     {
       "registry_type": "npm",

docs/guides/publishing/github-actions.md

@@ -254,7 +254,7 @@ Keep your package version and server.json version in sync:
 - name: Update server.json version
   run: |
     VERSION=${GITHUB_REF#refs/tags/v}
-    jq --arg version "$VERSION" '.version_detail.version = $version' server.json > tmp.json
+    jq --arg version "$VERSION" '.version = $version' server.json > tmp.json
     mv tmp.json server.json
 ```
 

docs/guides/publishing/publish-server.md

@@ -47,9 +47,7 @@ This creates a `server.json` with auto-detected values. You'll see something lik
   "$schema": "https://static.modelcontextprotocol.io/schemas/2025-07-09/server.schema.json",
   "name": "io.github.yourname/your-server",
   "description": "A description of your MCP server",
-  "version_detail": {
-    "version": "1.0.0"
-  },
+  "version": "1.0.0",
   "packages": [
     {
       "registry_type": "npm",