[roadmap] Improve startup diagnostics and troubleshooting docs

[latencyong-design]

Goal: make failed startup cases easier to diagnose from a public issue.

Scope:

• document common ProxyBridge path and permission failures;
• document how to verify the scheduled task points to the current runner;
• include redaction guidance for proxy URLs and local paths.

Done when the README or a troubleshooting doc gives users a short checklist before opening a bug report.