Hide more DX Assistant context menu items when no spot is targeted

[ea4k]

Summary

• Follow-up to the earlier fix that hid the "Spot" submenu when the DX Assistant context menu is opened without a spot under the cursor.
• "Hide this spot"/"Hide these spots" and "Copy Callsign" are now left out of the menu entirely (instead of shown disabled) when there's no spot under the cursor.
• "Clear all" is now left out when there's nothing to clear (no visible spots, no hidden calls, no worked QSOs this session).
• "Show to map" is now left out when the table currently has no spots shown.

Test plan

• Right-click on a row with a spot in the DX Assistant table and confirm "Hide this spot", "Copy Callsign", and "Spot" submenu still appear.
• Right-click on empty table space (or the header) and confirm those items are absent, not just greyed out.
• With an empty spot list, right-click and confirm "Clear all" / "Show to map" are absent; add spots and confirm they reappear.

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Generated by Claude Code

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud