bug(theme): do not drop structural refresh while theme watcher in flight

[ZhuchkaTriplesix]

Parent

Part of #463

Severity

Medium

Problem

When a debounced refresh fires while _refreshInFlight is true, _triggerRefresh returns immediately after _pendingStructural was already cleared. That refresh is lost with no reschedule. If the skipped refresh carried structuralChange: true, loadAvailableThemes(reloadExtensions: false) may run next and leave LocalExtensionRegistry stale until another install/uninstall.

Evidence

• lib/core/theme/theme_folder_watcher.dart (~91–107)
• Bugbot review dev vs main (2026-07-27)

Acceptance

• Refresh requested during in-flight run is queued and executed after
• Structural flag is OR’d across coalesced events (not lost)
• No infinite refresh loop

Suggested fix

Keep _pendingRefresh / _pendingStructural |= structural; when in-flight ends, if pending, schedule another _triggerRefresh.

[ZhuchkaTriplesix]

Fixed in #469 (merged to dev).