Add shared client-side virtualization for large job lists and dropdowns

[DaKheera47]

Summary

• add @tanstack/react-virtual and a shared client-side virtualization layer for window-scrolled and element-scrolled lists
• virtualize the main jobs list in JobListPanel while preserving existing selection, styling, routing, and window scroll behavior
• refactor JobCommandBar to use a flattened virtualized row model for lock suggestions and results with deferred query handling
• update SearchableDropdown to use the shared virtualized listbox path so existing large-option consumers scale automatically
• add measurement/test helpers and update client tests for offscreen rendering, keyboard navigation, and virtual scrolling

Testing

• ./orchestrator/node_modules/.bin/biome ci .
• npm run check:types:shared
• npm --workspace orchestrator run build:client
• npm --workspace orchestrator run test:run -- src/client/pages/orchestrator/JobListPanel.test.tsx src/client/pages/OrchestratorPage.test.tsx src/client/pages/orchestrator/JobCommandBar.test.tsx src/components/ui/searchable-dropdown.test.tsx
• npm --workspace orchestrator run check:types (fails due to existing missing undici resolution in src/server/api/routes/test-utils.ts)
• npm --workspace gradcracker-extractor run check:types (fails due to existing missing extractor dependencies/config)
• npm --workspace ukvisajobs-extractor run check:types (fails due to existing missing extractor dependencies/config)
• npm --workspace orchestrator run test:run (fails due to the existing undici/extractor environment issues above)

[Copilot]

Pull request overview

This PR introduces a shared client-side virtualization layer (based on @tanstack/react-virtual) and applies it to large, frequently-rendered UI surfaces (jobs list, command bar results, and searchable dropdown options) to reduce DOM mount cost while preserving existing UX.

Changes:

• Add @tanstack/react-virtual and a shared useVirtualizedList abstraction supporting window- and element-scrolled virtualization (with JSDOM scroll fallbacks).
• Virtualize JobListPanel (window scroll) and refactor JobCommandBar + SearchableDropdown to render virtualized rows/options with updated keyboard navigation and tests.
• Add DOM measurement + virtualization test helpers and update/extend client tests for offscreen rendering and virtual scrolling.

Reviewed changes

Copilot reviewed 18 out of 19 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
package-lock.json	Adds @tanstack/react-virtual + @tanstack/virtual-core lock entries.
orchestrator/package.json	Declares @tanstack/react-virtual dependency for the client.
orchestrator/src/setupTests.ts	Replaces ad-hoc ResizeObserver stub with shared DOM measurement mocks.
orchestrator/src/client/lib/virtual-list.ts	New shared virtualization hook wrapping TanStack (window/element modes + JSDOM scrollToFn support).
orchestrator/src/components/ui/virtualized-listbox.tsx	New hook to apply shared virtualization to listbox-like element scroll containers.
orchestrator/src/components/ui/searchable-dropdown.tsx	Refactors dropdown to use virtualized listbox rendering and custom keyboard navigation.
orchestrator/src/components/ui/searchable-dropdown.test.tsx	Adds tests ensuring large option sets remain virtualized and keyboard selection works.
orchestrator/src/client/test/dom-measurement.ts	New measurement helpers/mocks (ResizeObserver + rect/scroll utilities).
orchestrator/src/client/test/virtualization.ts	New helper to simulate window virtualization in tests (viewport + scroll).
orchestrator/src/client/pages/orchestrator/virtualizedList.ts	Adds a local element-virtualization wrapper used by the command bar.
orchestrator/src/client/pages/orchestrator/virtualizedList.test-utils.ts	Adds test utilities to mock rects/ResizeObserver for element virtualizer sizing.
orchestrator/src/client/pages/orchestrator/useScrollToJobItem.ts	Switches scroll-to-job behavior from DOM querying/scrollIntoView to virtualizer scrollToIndex.
orchestrator/src/client/pages/orchestrator/JobListPanel.tsx	Virtualizes the main jobs list (window scroll) and exposes a scroll handle via forwardRef.
orchestrator/src/client/pages/orchestrator/JobListPanel.test.tsx	Extends tests to validate virtualization and offscreen row rendering on scroll.
orchestrator/src/client/pages/orchestrator/JobCommandBar.utils.ts	Introduces a flattened “row model” to support virtualized command bar rendering.
orchestrator/src/client/pages/orchestrator/JobCommandBar.tsx	Refactors command bar to render virtualized rows (locks + results) with deferred query handling.
orchestrator/src/client/pages/orchestrator/JobCommandBar.test.tsx	Updates tests for async rendering/virtualization and keyboard navigation across offscreen items.
orchestrator/src/client/pages/OrchestratorPage.tsx	Wires JobListPanel scroll handle into useScrollToJobItem for programmatic scrolling.
orchestrator/src/client/pages/OrchestratorPage.test.tsx	Updates mocks/assertions to account for ref-based list scroll behavior.

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