perf(trees): gate QueryaAnimatedExpand / AnimatedContainer for large trees and Motion Off #726

Problem

Parent: #723

Native trees wrap sections in QueryaAnimatedExpand → AnimatedSize (connection expand, Databases, schemas, object groups). During the animation Flutter re-layouts the growing child every frame.

SDUI explicitly avoids height morph on the flat list because it fights itemExtent and costs FPS.

_PgTreeRow also uses AnimatedContainer for selection fill on every row.

Proposal

1. When Motion is Off / OS reduce-motion: snap expand (already mostly via duration tokens) — verify zero AnimatedSize ticks.
2. When expanding a node with child count above a threshold (e.g. > 24), skip height morph (instant show) even on Full motion — same spirit as SDUI.
3. Optional: selection highlight without AnimatedContainer when Reduced/Off or when using flattened list.
4. Keep chevron rotation (cheap) for feedback.

Acceptance

• Large expand (100+ tables) does not run multi-frame AnimatedSize layout on Full motion (or documents intentional skip)
• Motion Off: expand/collapse is instant with no leftover controllers
• Profile timeline attached for before/after on a large PG schema

Files

• lib/core/motion/querya_animated_expand.dart
• connections_panel_* expand sites
• _PgTreeRow / SDUI row decoration