Remove unused findSessionID function

[Fuabioo]

Problem

The findSessionID function in internal/cli/resume.go (lines 78-117) is defined but never called anywhere in the codebase.

Evidence

// findSessionID finds the full session ID for a given short or full ID.
func findSessionID(id string) (string, error) {
    // 40 lines of implementation...
}

The runResume function at line 30 calls findConversationFile(id) instead.

Impact

This is ~40 lines of dead code. It may have been a previous implementation that was replaced but not cleaned up.

Suggested Fix

Delete the findSessionID function. This is a simple cleanup task.

Files: internal/cli/resume.go:78-117