Fix sidebar virtual scroll anchoring

[nwparker]

Summary

• Preserve sidebar scroll from live virtual-row DOM keys before sleep, delete, and group collapse mutations
• Ignore stale TanStack Virtual measurements for disconnected/mismatched row elements
• Avoid sleep-triggered PTY exits bumping worktree activity while keeping the marker outside Zustand render state

Verification

• Electron CDP: right-click Sleep on bottom workspace nwparker/orca-launchctl-env: targetTop 220.00 -> 219.87, maxOverlapAfter 0, shutdown functions stubbed so no real worktree was touched
• Electron CDP: stubbed context-menu Delete on bottom workspace: delete handler invoked, next row corrected to ~220px, maxOverlapAfter 0, no disk deletion
• Electron CDP: grouped repo section collapse/expand near bottom: maxOverlapCollapsed 0, maxOverlapExpanded 0
• pnpm typecheck
• pnpm lint
• pnpm exec vitest run --config config/vitest.config.ts src/renderer/src/components/sidebar/sleep-worktree-flow.test.ts src/renderer/src/components/sidebar/delete-worktree-flow.test.ts src/renderer/src/components/sidebar/worktree-list-groups.test.ts