Previously, Claude Code's .mcp.json would silently override OpenCode user
config when MCP server names collided. This was unexpected behavior since
users expect their explicit OpenCode configuration to take precedence.
Changes:
1. Swapped merge order: Claude Code .mcp.json is now merged BEFORE user
config, so user config wins on collision
2. Added warning log when user config overrides a Claude Code MCP server:
'warning: MCP server X from user config overrides Claude Code .mcp.json'
3. Added comprehensive tests for collision scenarios
Fixes#2946
YeonGyu-Kim