Fix playground t-ruby-wasm integration issues

[yhk1038]

Problem

The playground's t-ruby-wasm integration has issues that need to be addressed for a reliable user experience.

Current Architecture

The playground uses CDN-loaded WASM files:

• T-Ruby library: @t-ruby/wasm@0.0.8 from jsdelivr
• Ruby WASM runtime: @ruby/wasm-wasi@2.7.1
• Ruby binary: @ruby/3.4-wasm-wasi@2.7.1

Issues to Fix

1. Network failures - No retry logic for CDN fetch failures
2. Timeout issues - 30-second compile timeout may be too tight
3. Memory management - No cleanup of loaded files between compiles
4. Error handling - Generic error messages need improvement
5. Worker lifecycle - No cleanup on component unmount

Files Affected

• src/lib/ruby-wasm.ts - WASM loader and worker management
• src/pages/playground.tsx - React component

Acceptance Criteria

• Playground loads reliably
• Compilation works correctly
• Error messages are user-friendly
• Verification tests pass