feat: add MCP Apps example servers module

Wire up 13 MCP Apps servers from the @modelcontextprotocol/server-* packages:
- budget-allocator: Interactive budget allocation UI
- cohort-heatmap: Customer retention heatmap
- customer-segmentation: Scatter chart with clustering
- map: Interactive 3D globe viewer (CesiumJS)
- pdf: Interactive PDF viewer
- scenario-modeler: SaaS business projections dashboard
- shadertoy: Real-time GLSL shader renderer
- sheet-music: ABC notation to sheet music visualizer
- system-monitor: Real-time OS metrics display
- threejs: 3D scene renderer
- transcript: Live speech transcription
- video-resource: Binary video streaming via MCP resources
- wiki-explorer: Wikipedia link graph visualization

Each server is mounted at /{slug}/mcp and shares the same OAuth
authentication as the main MCP server.

Also updates the splash page to dynamically list all available
example servers.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jerome3o-anthropic