Fix path traversal vulnerability in FilterService.GetFilterJaml

[Copilot]

The path traversal protection in GetFilterJaml was incomplete. Path.GetFileNameWithoutExtension("../../../etc/passwd.jaml") returns "../../../etc/passwd", leaving path separators intact since they're valid filename characters on some platforms.

Changes

• Use Path.GetFileName() before Path.GetFileNameWithoutExtension() to strip directory components first
• Add explicit validation that sanitized name contains no path separators after processing

// Before: vulnerable to path traversal
var safeName = Path.GetFileNameWithoutExtension(filterId);

// After: strips directory parts, then extension
var safeName = Path.GetFileNameWithoutExtension(Path.GetFileName(filterId));
// Then validate no separators remain
if (safeName.Contains(Path.DirectorySeparatorChar) || safeName.Contains(Path.AltDirectorySeparatorChar))
    return string.Empty;

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