perf(qa): Connections tree DevTools checklist @ 120 Hz (expand, scroll, filter) #727

Problem

Parent: #723

docs/perf-baseline.md already lists tree expand and high-Hz budgets, but we need a repeatable capture for the current native tree before/after FPS fixes so regressions are visible.

Proposal

Add a short Connections-tree section (or checklist issue runbook) that must be run on profile builds:

1. Cold expand PG connection → Databases → schema → Tables (large DB).
2. Scroll outer sidebar with 3+ connections expanded.
3. Type in Tables filter (debounce expectation).
4. Rapid leaf selection (10 clicks).
5. Motion Full vs Off comparison.

Attach DevTools Performance screenshots / frame charts to the epic or child PRs. Use QUERYA_REFRESH_OVERLAY=true on a 120 Hz display.

Acceptance

• Checklist checked into docs (or linked from perf-baseline)
• Baseline capture filed on this epic before major tree flatten lands
• Post-fix capture shows build+raster within budget for scenarios 1–4