fix: Omit RequestedFrameworks telemetry property when empty

[Copilot]

The check-start telemetry event was sending RequestedFrameworks="" when no --tfm options were specified, resulting in noisy/unusable data.

Changes

• Conditionally include RequestedFrameworks property only when frameworks are present after filtering
• When null/empty input or no frameworks match the regex pattern, omit property entirely from telemetry event

// Before: always sent property, even with empty string
_telemetry.TrackEvent("check-start", [("RequestedFrameworks", frameworks)], []);

// After: omit property when no frameworks to report
var properties = string.IsNullOrEmpty(frameworks)
    ? new (string, string)[] { }
    : new (string, string)[] { ("RequestedFrameworks", frameworks) };
_telemetry.TrackEvent("check-start", properties, []);

Framework filtering logic (regex, sorting, truncation) remains unchanged.

Original prompt

---

This section details on the original issue you should resolve

<issue_title>[Analytics] RequestedFrameworks property not returning values in uno-check/check-start event</issue_title>
<issue_description>### Current behavior 🐛

RequestedFrameworks property not returning values in uno-check/check-start event

Expected behavior 🎯

</issue_description>

Comments on the Issue (you are @copilot in this section)

@Jen-Uno https://github.com/unoplatform/private/blob/master/Telemetry-Docs/Telemetry.md

• Fixes unoplatform/uno-private#1498

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