feat: implement plugin infrastructure for rendering engines

Added comprehensive plugin system for independent JavaScript UI development:

**Plugin Infrastructure:**
- Extended existing MarkiTect plugin system with RenderingEnginePlugin base class
- Added RENDERING plugin type to PluginType enum
- Created RenderingConfig for asset management and deployment
- Implemented RenderingEngineManager for plugin discovery and lifecycle

**TestDrive JSUI Plugin:**
- Extracted JavaScript UI components to independent testdrive-jsui plugin
- Created standalone development environment (no Python required)
- Implemented compass-positioned control panels (NW, NE, E, SE)
- Added clean JSON configuration interface for Python↔JavaScript data transfer

**Asset Management:**
- Development mode: serve assets directly from plugin source directory
- Production mode: deploy to _markitect/plugins/[plugin-name]/ structure
- Configurable asset URLs and deployment strategies
- Support for external dependencies (CDN resources)

**Standalone Development:**
- testdrive-jsui/test.html for browser-based development
- Package.json with npm scripts for development server
- Complete separation of JavaScript development from Python environment
- Hot reload and standard web development workflow

**Integration Demo:**
- demo_plugin_integration.py showcasing all plugin capabilities
- Standalone, plugin discovery, production deployment examples
- Asset URL generation for different deployment modes

This enables JavaScript-first development while maintaining clean integration
with the MarkiTect Python ecosystem. Developers can now work on UI components
independently using standard web development tools and workflows.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

testdrive-jsui/test-documents/sample.md

@@ -0,0 +1,57 @@
+# TestDrive JSUI Sample Document
+
+This is a sample markdown document for testing the TestDrive JavaScript UI plugin.
+
+## Features to Test
+
+### Basic Editing
+- Click any section to edit it
+- Use the save button to download your changes
+- Reset button restores original content
+
+### Control Panels
+- **Contents Control** (Northwest): Document outline and navigation
+- **Status Control** (East): Current document statistics
+- **Debug Control** (Southeast): Development information and logs
+- **Edit Control** (Northeast): Main editing actions
+
+### Markdown Support
+Test various markdown elements:
+
+**Bold text** and *italic text*
+
+> This is a blockquote
+> with multiple lines
+
+```javascript
+// Code blocks with syntax highlighting
+function testFunction() {
+    console.log("Hello from TestDrive JSUI!");
+    return true;
+}
+```
+
+### Lists
+1. Numbered list item one
+2. Numbered list item two
+3. Numbered list item three
+
+- Bullet list item
+- Another bullet item
+  - Nested bullet item
+  - Another nested item
+
+### Tables
+
+| Feature | Status | Notes |
+|---------|--------|--------|
+| Section editing | ✅ Working | Click to edit |
+| Asset loading | ✅ Working | External scripts |
+| Configuration | ✅ Working | JSON interface |
+| Controls | 🚧 Testing | Compass positioning |
+
+### Links and Images
+Visit the [Markitect repository](https://github.com/markitect/markitect) for more information.
+
+---
+*Test document for TestDrive JSUI plugin development*