implement openings page

src/components/DiscussionPopupForm.tsx

src/components/LabPopup.css

src/components/LabPopup.tsx

src/components/OpeningListItem.css

src/components/OpeningListItem.tsx

src/components/OpeningPopup.tsx

src/components/OpeningsList.css

src/components/OpeningsList.tsx

src/components/OpeningsPopupForm.tsx

src/components/Popup.css

src/components/PopupForm.css

src/components/form/SelectInput.tsx

src/contexts/OpeningsContext.tsx

src/main.tsx

src/pages/OpeningsPage.css

src/pages/OpeningsPage.tsx

src/services.ts

src/types.ts

src/utils.ts