Add troubleshooting section for common user issues

[gaojude]

Users on Windows have been hitting a module resolution error when npx tries to load the MCP server. The error shows up as ERR_MODULE_NOT_FOUND pointing to paths with parentheses like (cache-components) in the directory structure. This happens because npx's cache can get stale or corrupted, particularly on Windows where parentheses in paths can cause module resolution issues.

The fix is simple - clearing the npx cache resolves it - but users had no way to discover this solution on their own. They'd see the cryptic error and have to reach out for support or dig through issues.

This adds a troubleshooting section to the README documenting both this npx cache issue and the "No server info found" error (which happens when users try to use runtime diagnostic tools without a running dev server). The guidance is intentionally concise - just tells users to clear the cache without overwhelming them with platform-specific commands.

Now users can self-serve these common fixes instead of getting stuck during setup.