feat: Add context awareness and intelligent improvements to MCP tools

Based on Claude Code Task feedback, this commit implements major improvements:

Context Awareness:
- Add NixOSContext class to track state between tool calls
- Tools can now reference previous search results (e.g., show(1) for first result)
- versions() and compare() can use context when package name omitted
- install() auto-detects appropriate installation method

User Experience:
- Add concise parameter to reduce output verbosity for experienced users
- Deduplicate search results and group multiple versions of same package
- Improve error messages with 'did you mean' suggestions
- Better which() tool accuracy with query prioritization

Code Quality:
- Add comprehensive test suite (376 tests total)
- Standardize output formatting with format_output() function
- Update CLAUDE.md with code quality commands
- Fix linting issues (ruff check passes)

These changes make the MCP tools significantly more intelligent and user-friendly,
reducing repetitive typing and providing helpful suggestions when things go wrong.

Author: jamesbrink

CLAUDE.md

@@ -62,12 +62,27 @@ mypy mcp_nixos/
 
 ## Testing Approach
 
-- 367+ async tests using pytest-asyncio
+- 376+ async tests using pytest-asyncio
 - Real API calls (no mocks) for integration tests
 - Unit tests marked with `@pytest.mark.unit`
 - Integration tests marked with `@pytest.mark.integration`
 - Tests ensure plain text output (no XML/JSON leakage)
 
+## Code Quality Commands
+
+When making changes, always run:
+```bash
+# Lint and format
+ruff check mcp_nixos/ --fix
+ruff format mcp_nixos/
+
+# Run tests
+pytest tests/
+
+# Type check (note: some type issues are known and non-critical)
+mypy mcp_nixos/
+```
+
 ## Local Development with MCP Clients
 
 Create `.mcp.json` in project root (already gitignored):