Subject

I would like to contribute to the project

Description

Problem

The current error message emitted during TLS setup with SSL_TYPE=self-signed
is ambiguous:

File A or B or C does not exist

This can be misread as a single missing file, while the actual requirement
is that all files must exist.

Solution

This PR keeps the existing validation logic intact but improves the error
message by:

• Explicitly stating that one or more required files are missing
• Listing the expected file paths

Impact

• No behavioral changes
• Improved UX and debuggability
• No security impact