fix(i18n): refresh all localized bindings live on language switch

[keyldev]

• SetLanguage raised PropertyChanged("Item[]"), a WPF-ism Avalonia ignores
• Avalonia's INPC accessor re-reads only on PropertyName=="Item" or empty; string-keyed indexer bindings use the CLR name "Item", not "Item[]"
• bottom nav / sidebar (persistent controls) stayed stale until restart; pages only looked translated because they rebuild on navigation
• raise PropertyChanged(string.Empty) — "all changed" — so every binding on Localizer.Instance re-reads instantly

Summary

Fixing issue #8

• SetLanguage raised PropertyChanged("Item[]"), a WPF-ism Avalonia ignores
• Avalonia's INPC accessor re-reads only on PropertyName=="Item" or empty; string-keyed indexer bindings use the CLR name "Item", not "Item[]"
• bottom nav / sidebar (persistent controls) stayed stale until restart; pages only looked translated because they rebuild on navigation
• raise PropertyChanged(string.Empty) — "all changed" — so every binding on Localizer.Instance re-reads instantly

Related

Type

• Bug fix
• Feature
• Refactor / cleanup
• Docs / CI
• Other:

Checklist

• Builds with 0 warnings (TreatWarningsAsErrors=true).
• Tests pass (dotnet test); new Core logic has unit tests.
• No layering violation — App references Core only (Infrastructure / Video / Devices wired via DI in a head).
• Scope stays within one phase (didn't pull work from a later phase's "Не входит").
• README / docs updated if public commands, options, or setup changed.

Platforms tested

• Windows
• Linux
• macOS
• Android
• iOS
• CI build only

Screenshots / notes