feat: web extension

[andi1984]

Implements web extension compatibility to enable the TinyPNG extension to work in VSCode's web environment (vscode.dev). This addresses issue #232.

Key changes:

• Created tinify-web.ts: Web-compatible TinyPNG API wrapper using Fetch API instead of Node.js tinify library
• Created extension.web.ts: Web-compatible extension entry point using VSCode's FileSystem API instead of Node.js fs module
• Added webpack bundling configuration for both web and Node.js targets
• Updated package.json with browser field and webpack build scripts
• Added webpack, webpack-cli, and ts-loader as dev dependencies
• Updated tsconfig.json to include DOM types for web APIs

Technical details:

• Web version uses direct HTTP calls to TinyPNG API via fetch()
• Replaced fsPath file access with VSCode FileSystem API
• Git stage compression feature not available in web version (requires child_process which is Node.js only)
• Both desktop and web versions are built and bundled separately

Build outputs:

• dist/web/extension.web.js: Web extension bundle (5.7 KB)
• dist/node/extension.js: Node.js extension bundle (250 KB)

Resolves #232

[andi1984]

Can not be done as TinyPNG API does not seem to support CORS.