perf(trees): stop selection InheritedWidget from rebuilding entire expanded tree

[ZhuchkaTriplesix]

Problem

Parent: #723

_ConnectionsTreeSelectionScope is an InheritedWidget. Any leaf that calls of(context) rebuilds when any selection field changes (updateShouldNotify compares all driver selections).

With several connections expanded, selecting one table can rebuild large parts of the sidebar tree.

Combined with AnimatedContainer selection chrome on _PgTreeRow / SDUI rows, that becomes paint+layout work on many rows for one click.

Proposal

1. Prefer a ValueListenable / ListenableBuilder (or selector) so only the previous and newly selected rows rebuild.
2. Or split scopes per connection id so cross-driver noise does not fan out.
3. Consider DecoratedBox + instant style when Motion Off/Reduced instead of animating every selection.

Acceptance

• Selecting a table does not rebuild unrelated expanded connection subtrees (verify with Flutter rebuild highlighter / DevTools)
• Selection highlight still correct for PG/MySQL/SQLite/Extension/Redis/Mongo
• No FPS spike on rapid click-through of leaves @ 120 Hz

Files

• lib/features/connections/connections_panel.dart (_ConnectionsTreeSelectionScope)
• _PgTreeRow consumers / SDUI isNodeSelected

[ZhuchkaTriplesix]

Fixed in #736