perf(desktop): lazy-mount sidebar session trees

[likun666661]

Summary

• lazy-mount linked child-session trees instead of recursively mounting every Swarm descendant
• keep only the active session ancestor chain expanded so externally selected child sessions remain visible
• preserve Astryx disclosure chrome with a zero-layout sentinel while collapsed
• add regression coverage for collapsed descendants, active-child expansion, and stale-session presentation

Why

The sidebar recursively rendered every linked child session even when its parent appeared collapsed. On a real workspace with 36 root sessions and 118 Swarm child sessions, the expanded rail kept roughly 10,000-12,000 DOM nodes and thousands of listeners alive. Any navigation or selection then paid React, style, and layout costs across that tree.

Local CDP evidence

Metric	Before	After
Rendered session rows	154	36
DOM elements	about 10,000-12,000	3,884
Event listeners	about 3,572-4,600	1,293
Renderer JS heap	about 33 MB	18.8 MB
Navigation click input delay	-	about 0.3 ms

The 118 child rows are now absent from the DOM until their parent is expanded. Eighteen roots retain disclosure controls.

Validation

• npm --workspace @maka/ui run typecheck
• npm --workspace @maka/desktop run typecheck
• npm --workspace @maka/desktop run build
• targeted sidebar suites: 27 tests passed
• rebuilt and installed the arm64 Desktop app; verified the real user workspace through CDP