test(mcp): add comprehensive test coverage for MCP server

Add test infrastructure for MCP server components:
- server_test.go: Server lifecycle, protocol handlers, request dispatch
- tools_test.go: All 6 tools with edge cases and extended fixtures
- types_test.go: JSON serialization/deserialization for all types

Coverage: 89.7% overall (excluding stdin-based ServeStdio function)
- All tool functions: 100%
- Protocol handlers: 100%
- Type helpers: 100%

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <[email protected]>

Author: shivasurya