Theme: миграция P0 workbench surfaces (#42)

[ZhuchkaTriplesix]

Summary

Sub-task of #42: миграция P0 workbench surfaces на theme tokens (один PR).

Файлы (строго этот список)

• lib/features/connections/connections_panel_sidebar.dart
• lib/features/main_screen/workspace_panel.dart
• lib/features/main_screen/main_screen.dart
• lib/features/main_screen/sql_editor_chrome.dart
• lib/features/main_screen/workspace_empty_hero.dart
• lib/features/main_screen/results_tab.dart

Правила

• Использовать context.workbench / Theme.of(context).colorScheme (Theme: QueryaThemeScope (InheritedWidget) #54)
• Не добавлять новые QueryaColors.* (deprecated)
• Glow в SqlEditorChrome — workbench.accent с alpha

Acceptance criteria

• Grep P0 files: zero QueryaColors (кроме import deprecated shim если есть)
• Manual: connections tree + SQL tab + results grid на dark default и imported theme
• PR ссылается на Theme: миграция workbench UI на design tokens #42

Зависимости

• Theme: QueryaThemeScope (InheritedWidget) #54, Theme: runtime-тема в QueryaApp (ShadcnApp + materialTheme) #41
• Parent: Theme: миграция workbench UI на design tokens #42

Оценка

~1–2 дня

[ZhuchkaTriplesix]

Delivered on dev in the Theme system milestone. See docs/theme.md and PRs #66, #74–#83.