Harden Windows startup health checks

[blaze818]

Summary

• add startup health checks for required Codex MCP servers and Graphify health
• avoid extra shell layers when invoking Codex CLI on Windows
• preserve corrupt session metadata files instead of silently discarding them

Verification

• npm.cmd test -- test/codex-auth.test.ts test/startup-health.test.ts
• npm.cmd test
• npm.cmd run build
• local secrets scan before push returned no findings