test: add component tests for DashboardLayout, DataTable, Combobox, MilestoneTimeline, ShipmentSummaryPrint

[Raven062]

Summary

Closes issues Navin-xmr#739, Navin-xmr#740, Navin-xmr#741

Adds component tests with zero previous coverage for five components:

Component	Test File	Issue
DashboardLayout.tsx	src/components/layout/DashboardLayout.test.tsx	Navin-xmr#739
DataTable.tsx (common)	src/components/common/DataTable/DataTable.test.tsx	Navin-xmr#740
Combobox.tsx	src/components/ui/Combobox.test.tsx	Navin-xmr#740
MilestoneTimeline.tsx	src/components/shipment/MilestoneTimeline/MilestoneTimeline.test.tsx	Navin-xmr#741
ShipmentSummaryPrint.tsx	src/components/shipment/ShipmentSummaryPrint/ShipmentSummaryPrint.test.tsx	Navin-xmr#741

What's covered

DashboardLayout — initial render, nav items, Outlet rendering, active route highlighting, sidebar collapse/expand, nav group accordion, favorites (add/remove/persist/restore from localStorage), mobile sidebar dialog (role=dialog, aria-modal), keyboard shortcuts modal, enterprise node status widget.

DataTable — column headers, data rows, loading skeleton, empty state with CTA, sorting (asc/desc/reset, numeric, non-sortable columns), row click callback, pagination (page buttons, aria-current, prev/next disabled states, item range summary).

Combobox — initial render, controlled value, opening dropdown, filtering (case-insensitive), option selection (onChange + onSelectOption), keyboard navigation (ArrowDown/Up/Enter/Escape), clear button, loading state, disabled state, outside click.

MilestoneTimeline — render, filter pills (All/Completed/In Progress/Upcoming), empty state after filtering, clear filter, zoom controls (in/out/disabled at limits/reset), expandable milestone details (notes, sensor readings), blockchain link for completed milestones.

ShipmentSummaryPrint — portal rendering, all metadata fields (id, status, sender, receiver, tracking, carrier, priority, dates), milestone table, cost breakdown, payment info, sensor snapshot, notes, delivery proof, Stellar TX hash, print+close lifecycle (window.print called after 200 ms delay, onClose fired once).

Testing approach

• Vitest + React Testing Library, matching the project's established patterns
• Behavior-focused assertions (what the user sees/can do), not implementation details
• Heavy dependencies (realtimeService, ToastContext, WalletContext, useTheme, authApi) mocked at the module level
• window.print and HTMLElement.prototype.scrollIntoView stubbed for jsdom compatibility

What was tested

pnpm run test run locally; all five new test files pass.