Add next-themes light/dark/system theming with an accessible toggle
in every header, and close out an a11y pass across the viewer app:
skip-to-content link, main landmarks and heading hierarchy on every
route, focus-trapped dialog semantics for the photo viewer modals,
aria-label/live-region coverage for dynamic messages and icon
buttons, and dark: variants for previously light-only colors.
This commit introduces several new scripts for managing database operations, including user creation, permission grants, and data migrations. It also adds new documentation files to guide users through the setup and configuration processes. Additionally, the project structure is updated to enhance organization and maintainability, ensuring a smoother development experience for contributors. These changes support the ongoing transition to a web-based architecture and improve overall project functionality.