feat(convert): translate MCP server config to .gemini/settings.json

[duyluann]

Problem

MCP server configuration in .claude/settings.json (mcpServers) is Claude Code-specific. No equivalent exists in GitHub Copilot or OpenAI Codex. Gemini CLI has its own mcpServers block in .gemini/settings.json with a structurally similar format.

Proposed Solution

For Gemini CLI target, /convert should:

1. Read mcpServers from .claude/settings.json
2. Translate each entry to Gemini CLI's mcpServers format
3. Merge into the generated .gemini/settings.json

For Copilot and Codex targets, note MCP servers in the unsupported section with a workaround suggestion (expose via OpenAPI spec and register as function tools).

Acceptance Criteria

• Gemini CLI target generates .gemini/settings.json with translated mcpServers
• Field mapping documented (Claude → Gemini format differences)
• Copilot/Codex targets include workaround note

Ref: #11