Send custom User-Agent on all MCP server API calls

[mars-steven]

Summary

• Adds a User-Agent: gemini-mcp/<pkg-version> (node/<node-version>) header to every Gemini API request made from the MCP server (both publicGet and authenticatedPost in packages/mcp-server/src/client/http.ts).
• Version pulled from package.json via createRequire so it stays in sync with release bumps. Bumped to 1.0.1.

Test plan

• npx tsc --noEmit clean
• npm test — 22/22 pass
• Confirm User-Agent shows up in upstream access logs after deploy

🤖 Generated with Claude Code

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