Migrate the frontend to ESLint 9, add `eslint.config.mjs`, and replace various `any` types with more specific or safer alternatives across the codebase.
- Update `package.json` with new ESLint and TypeScript-ESLint dependencies
- Replace `any` with `Record<string, unknown>` or specific types in `TemplatePicker`, `Editor`, and `FileBrowser`
- Improve error handling in `TeamSettings` and `Templates` using type guards
- Add explicit type imports for Excalidraw elements in `Editor.tsx`
- Refactor `Modal.tsx` for cleaner conditional logic
- Add `check` script to `package.json` for type checking
- Fix go.mod Go version from invalid 1.25.7 to 1.23
- Fix Dockerfile golang image from 1.25 to 1.23
- Add window.matchMedia mock for jsdom themeStore tests
- Exclude e2e/ from Vitest to prevent Playwright test conflicts
- Add frontend test step to both CI workflows
Tomas Dvorak