perf(trees): flatten native connection tree into one virtualized list (drop nested shrinkWrap) #724

Problem

Parent: #723

lazyConnectionTreeList (connections_panel.dart) builds either:

• a full Column when itemCount ≤ 24, or
• ListView.builder(shrinkWrap: true) capped to 14× row height

These sit inside QueryaAnimatedExpand → AnimatedSize, which itself sits inside the outer sidebar SliverList item for each expanded connection.

Effect: nested scrollables + shrink-wrap layout passes during expand and when scrolling the outer panel — high risk of dropped frames at 120/144 Hz with large schemas/table lists.

SDUI already flattens to a single ListView.builder and skips height morph for this reason.

Proposal

1. Flatten expanded native tree (connection → DB → schema → groups → leaves) into one virtualized list (prefer patterns like SDUI flatten, or Flutter TreeSliver if it fits desktop sidebar).
2. Remove nested ListView(shrinkWrap: true) under the outer CustomScrollView.
3. Keep fixed itemExtent (kConnectionTreeRowExtent) where possible.
4. Coordinate with visual parity #719 so one row widget serves native + SDUI.

Acceptance

• Expanding a PG database with hundreds of tables does not nest a shrink-wrapped ListView inside the sidebar SliverList
• Only viewport (+ cacheExtent) rows are built
• Profile @ 120 Hz: expand + scroll stay within budget (attach timeline screenshot)
• Existing selection / context menu / filter behavior preserved

Files

• lib/features/connections/connections_panel.dart (lazyConnectionTreeList)
• connections_panel_pg_tree.dart, _mysql, _sqlite, _mongo, _redis
• lib/core/sdui/sdui_tree_builder.dart (reference)