Plugins: defer VST3 editor creation until requested

[emaspa]

Changes

Elgato EQ 1.3.0.110 crashes when activation follows a VST3 editor view being created and released. OpenXLR did that while loading to check for editor availability.

• Defer view creation until the editor is actually requested, matching the scanner's existing behavior.
• Report a plugin with no compatible editor accurately after the open attempt.
• Add coverage for the deferred no-editor reply and a manual real-plugin lifecycle diagnostic.

Verification

• The original Elgato EQ reproduction changed from exit 134 to exit 0 after removing the load-time probe.
• The real plugin processed 60 cycles, opened and closed its editor under Xvfb, and unloaded with Wine host exit 0.
• Filtering a 440 Hz tone confirmed actual EQ processing, not just process survival.
• Native build passed with warnings treated as errors. Audio and CLAP tests passed all 16 cases; editor tests passed all 11 cases.
• Deployed locally and confirmed working. The running helper was verified against the rebuilt binary.

The plugin still fails if explicitly deactivated and reactivated after a view has been created. OpenXLR activates once per helper process, so its normal lifecycle does not take that path. The diagnostic documents it.

No version bump or release changes. Individual-plugin management is a separate change.