Overhaul the app's color system by replacing all hardcoded Tailwind color classes with semantic theme variables to ensure consistent theming across all components, pages, and tests.
Additional changes:
- Add assigned date support for order item status updates: add `assignedDate` field to the order item status PATCH API, implement server-side normalization/validation, and add corresponding tests
- Refactor purchase order PDF workflows to use the consolidated `purchase_orders.documents` field instead of the legacy separate `purchase_order_pdfs` collection
- Fix quote number parsing and formatting to support both dashed (Q-YYYY-MM-NNN) and dashless (QYYYYMMNNN) formats
- Rename `driver_pool` item status to `collection_pool` across the codebase
- Add null handling for order item quantities and pricing to display "—" for missing values
- Improve filter tab styling: make mobile tabs scrollable, prevent text wrapping, hide scrollbar
- Add new utility scripts, API routes, migrations, and polish small UI/UX fixes including tsconfig updates and theme hook improvements
