feat(examples): add debug-server for comprehensive SDK testing

[ochafik]

Superseded by #321

Summary

Adds a debug-server example that exercises all MCP Apps SDK capabilities for testing and debugging purposes.

Features

• Event log with expandable entries showing all SDK callbacks
• Callback tracking table showing registration status and invocation counts
• Host info display showing context, capabilities, container dimensions, and styles
• Message actions - send text and image messages
• Logging actions - debug, info, warning, error levels
• Model context updates - text, structured, and image content
• Display mode controls - inline, fullscreen, PiP
• Size controls - auto-resize toggle and manual resize buttons
• Server tool calls - configurable debug-tool with multiple content types

Code Quality Improvements

Addresses issues from code review:

Issue	Fix
Memory leak: setInterval	Store interval ID, cleanup in onteardown
Memory leak: auto-resize	Cleanup autoResizeCleanup in onteardown
Event listeners re-added on render	Use event delegation instead
XSS: incomplete HTML escaping	Added escapeHtml() that escapes & < > " '
Duplicated base64 constant	Extracted TEST_RED_PNG constant
Fire-and-forget sendLog	Added await and try/catch
package.json: runtime deps in devDeps	Moved cors/express to dependencies
package.json: missing fields	Added main, types, bin, exports

Testing

• Added to E2E tests in servers.spec.ts with dynamic masks for event log, callback table, and current size
• Added to generate-grid-screenshots.spec.ts for grid cell generation
• All E2E tests passing in Docker

Screenshots