Remove redundant npm link in favor of workspace dependencies

[Copilot]

The repository was using both npm workspaces and manual npm link commands via a postinstall script, causing unnecessary complexity.

Changes

• Added explicit workspace dependencies: Declared game-engine and chess-shared in client and server package.json dependencies
• Removed manual linking: Deleted scripts/link-packages.sh and updated postinstall to just build the game-engine
• Added Vite aliases: Configured path resolution for workspace packages in client bundler
• Updated workspace config: Added shared package to workspaces array

Before

# postinstall script
bash scripts/link-packages.sh  # 41 lines of manual npm link/unlink commands

After

# postinstall script  
npm run build:engine  # workspaces handle linking automatically

npm workspaces (enabled in root package.json) already creates symlinks in node_modules automatically when workspace packages are declared as dependencies. The manual linking was redundant.

Original prompt

#41

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