Add collapsible activity-sorted thread tree

[wizzoapp]

Summary

• add persisted chevron expansion for parent thread groups in the sidebar; chevron toggles only the group while parent row click still opens the thread
• sort active threads first, then by sidebar thread activity order; parent groups float by their most active descendant and children use the same ordering
• cover sort behavior and expansion-state persistence in web tests

Verification

• vp run --filter @t3tools/web test -- src/components/Sidebar.logic.test.ts src/uiStateStore.test.ts
• vp run --filter @t3tools/web build
• vp run typecheck
• vp check (passes; existing unrelated mobile unused-code warnings remain)
• factory pre-commit gate passed with clean Codex autoreview

Visual verification

• T3 preview could not attach: preview_open returned PreviewAutomationNoAvailableHostError. Reported as ADA-81.

Goes live on the next web redeploy after merge.

[chatgpt-codex-connector]

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Reviewed commit: 422986f182

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[adamfgr]

Auto-approved by wizzo-approve: all policy conditions verified against HEAD 578bffe.