✨ Set up GitHub Copilot instructions for enhanced AI-assisted development

[Copilot]

This PR establishes comprehensive GitHub Copilot instructions to provide AI-assisted development with accurate, contextually-appropriate code suggestions for the beets-plexsync project.

What's Added

Dual Location Coverage: Created instruction files in both .github/copilot-instructions.md and .copilot/instructions.md to ensure compatibility with different Copilot versions and configurations.

Comprehensive Project Context:

• Complete overview of the beets-plexsync plugin functionality (library sync, AI playlists, external imports)
• Architecture documentation with key files (plexsync.py, llm.py, matching.py, etc.) and their purposes
• Detailed dependency information including core libraries (beets, plexapi, pydantic) and LLM framework (agno)

Critical Development Constraints:

• Clear warning about NEVER modifying cache keys (SQLite integrity protection)
• API compatibility preservation requirements
• beets plugin convention compliance guidelines

Practical Code Patterns and Examples:

# Logging patterns using beets logger
self._log.debug("Debug message")

# Configuration access
value = self.config['setting_name'].get()

# Plex connection handling
plex = self.get_plex()
library = plex.library.section(self.config['library_name'].get())

# Caching implementation
cache = Cache(self.config['cache_file'].get())
result = cache.get(key) or expensive_operation()

Development Guidelines: Command creation patterns, error handling approaches, testing strategies (manual CLI testing), and file organization principles.

Why This Matters

The existing agents.md file provided context for Gemini/other AI assistants, but GitHub Copilot needed its own dedicated instruction files in the standard locations. These instructions will help Copilot:

• Understand the beets plugin architecture and conventions
• Respect critical constraints like cache key immutability
• Follow established patterns for logging, configuration, and API usage
• Generate contextually appropriate suggestions for this music library management domain

The instructions are crafted to maintain the project's architectural integrity while enabling more effective AI-assisted development workflows.

Fixes #101.

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.

[Copilot]

@arsaboo 👋 This repository doesn't have Copilot instructions. With Copilot instructions, I can understand the repository better, work faster and produce higher quality PRs.

I can generate a .github/copilot-instructions.md file for you automatically. Click here to open a pre-filled issue and assign it to me. I'll write the instructions, and then tag you for review.