fix(tabs): wrap QueryaTabStrip in horizontal scrollable and preserve GlobalKeys on tab count change

[ZhuchkaTriplesix]

Description

• Wraps QueryaTabStrip in built-in horizontal scrolling (SingleChildScrollView + IntrinsicWidth) with mouse wheel (PointerScrollEvent) and automatic smooth ensureVisible scrolling to selected tab.
• Incrementally updates GlobalKey and FocusNode lists in _syncTabState when tab count changes instead of resetting all keys, preserving existing widget state and avoiding unmounting.
• Eliminates 1-frame sliding indicator disappearance/flicker by keeping _indicatorReady = true on tab updates and smoothly animating the pill indicator to the new tab position.
• Wraps QueryaTabStrip in Expanded(child: Align(alignment: Alignment.centerRight, ...)) across workspace headers (mysql_workspace_home.dart, postgres_workspace_home.dart, sqlite_workspace_home.dart, extension_workspace_home.dart) preventing RenderFlex right overflows on narrow screen widths.
• Removes redundant outer SingleChildScrollView in sql_query_tab_bar.dart.
• Adds widget tests covering incremental key preservation, constrained horizontal scrolling, mouse wheel pointer scrolling, and auto-scroll to selected tab.

Closes #898