Convert Deno client to universal Node.js/Deno/Bun compatibility

[just-be-dev]

Summary

This PR converts the Deno-specific webview client to be universally compatible with Deno, Node.js, and Bun runtimes. The changes enable cross-platform usage while maintaining backward compatibility with existing Deno workflows.

• Configuration Migration: Replaced deno.json with package.json for npm ecosystem compatibility
• API Conversion: Converted all Deno-specific APIs to Node.js built-ins using node: prefix
• Import System: Implemented TypeScript configuration for extensionless imports with post-build processing
• Cross-Runtime Support: Added platform detection and fallback handling for unknown runtimes
• Binary Management: Enhanced binary downloading with cross-platform cache directory resolution
• Examples Update: Updated all examples to use new import paths and work with compiled JavaScript

Key Technical Changes

Runtime API Conversion

• Deno.Command → node:child_process.spawn
• Deno.env → process.env
• Deno.writeFile → node:fs/promises.writeFile
• Deno.readTextFile → node:fs/promises.readFile
• Deno.mkdir → node:fs/promises.mkdir
• Added platform detection for Bun with graceful fallbacks

Build System

• Created two-phase TypeScript compilation process
• Added fix-imports.js script to convert extensionless imports to .js extensions
• Configured TypeScript for extensionless source imports while maintaining Node.js ESM compatibility

Dependency Management

• Migrated from JSR dependencies to npm equivalents
• Replaced unavailable packages with compatible alternatives:
  • @bcheidemann/tracing → custom console logger
  • @gabriel/ts-pattern → ts-pattern

Test Plan

• Install dependencies: cd src/clients/deno && npm install
• Build the project: npm run build
• Test Node.js compatibility: node examples/simple.js
• Test Deno compatibility: deno run --allow-all examples/simple.ts
• Verify all examples compile and run successfully
• Check that webview creation and basic functionality works across runtimes
• Ensure binary downloading works on different platforms

Runtime Compatibility

• ✅ Node.js 18+ (fully supported with native APIs)
• ✅ Deno (backward compatible, can use TypeScript directly)
• ⚠️ Bun (limited support, may have issues with older versions)

Breaking Changes

None for existing Deno users - the package maintains full backward compatibility while adding Node.js/Bun support.