upgrading packages and fixing linting errors

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[Copilot]

Pull request overview

This PR upgrades multiple packages and fixes linting errors across the codebase. The main focus is on modernizing the code to follow TypeScript and React best practices, including the use of type imports, refactoring client-side rendering detection in portal components, and updating the ESLint configuration.

Changes:

• Upgraded multiple dependencies including Next.js (16.0.10 → 16.1.6), React (19.2.1 → 19.2.4), TypeScript ESLint tooling, and others
• Converted all type imports to use the type keyword prefix (e.g., import { type Foo })
• Refactored portal-based components (Modal, ConfirmationModal, ActionResponsePopup) to use useSyncExternalStore instead of useState + useEffect for client-side detection
• Replaced functional component wrappers for table headers with direct JSX elements
• Simplified state management in several components (buy.tsx, account.tsx, admin pages)
• Updated ESLint configuration to use flat config format with Next.js core-web-vitals
• Fixed apostrophe HTML entity in German text and formatting inconsistencies

Reviewed changes

Copilot reviewed 40 out of 41 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
package.json	Updated dependency versions and changed lint command from next lint to eslint .
package-lock.json	Lockfile updates for new package versions
eslint.config.mts	Simplified ESLint config using flat format with Next.js core-web-vitals
src/server/api/routers/*.ts	Added type keyword to type-only imports
src/pages/*.tsx	Added type keyword to imports and refactored state management
src/pages/buy.tsx	Refactored category filter state management to use overrides pattern
src/pages/index.tsx	Simplified error message handling logic
src/pages/account.tsx	Simplified pagination state, replaced computed date with React state
src/pages/admin/*.tsx	Simplified pagination logic and converted Legend components to JSX elements
src/components/**/*.tsx	Added type imports, refactored portal components, converted Legend to JSX
src/components/Layout/Modal.tsx	Replaced useState+useEffect with useSyncExternalStore
src/components/General/ConfirmationModal.tsx	Replaced useState+useEffect with useSyncExternalStore
src/components/General/ActionResponsePopup.tsx	Replaced useState+useEffect with useSyncExternalStore
src/components/Forms/UserForm.tsx	Simplified allow overdraw state management
src/components/Forms/ClearingAccountForm.tsx	Moved useEffect after useForm hook
src/components/FormElements/GroupOrderSplit.tsx	Added timeout cleanup to useEffect
src/components/FormElements/CategorySelector.tsx	Removed ESLint disable comments

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[Copilot]

The reset() function is called in a useEffect that depends on props.id, but the reset function from useForm is missing from the dependency array. This could lead to ESLint warnings and potential issues if the reset reference changes. Add reset to the dependency array: }, [props.id, reset]). Alternatively, if reset is stable (which it should be from useForm), add an ESLint disable comment with justification.

Suggested change

	}, [props.id])
	}, [props.id, reset])

[Copilot]

The defaultDisplayCategories object is computed on every render, which could cause performance issues if allRelevantCategories is large. Since this computation depends on data that changes with the query, consider wrapping it in useMemo to avoid unnecessary recomputation: const defaultDisplayCategories = useMemo(() => { ... }, [allRelevantCategories])