feat: enhance Spotify MCP playback controls and docs

[minhnld]

What

Improve playback tooling and docs across the Spotify MCP server, including stronger playback controls and liked-song support.

Key changes

• Add and wire new playback capabilities (including shuffle/repeat controls and next-track flow updates) in src/play.ts and command registration in src/index.ts
• Extend read/utility behavior for track state and supporting helpers in src/read.ts and src/utils.ts
• Update package scripts/dependencies in package.json
• Expand project and usage documentation in README.md
• Add PROJECT_GUIDE.md with implementation and usage guidance