Next 15 -> 16 upgrade and package updates

[18-th]

• Rename middleware.ts → proxy.ts and export function to match Next.js 16 convention
• Add revalidateTag second argument ("max") required in Next.js 16
• Remove stray internal Next.js import from linkUtils test
• Update tsconfig to add .next/dev/types (new dev output dir in Next.js 16)
• Upgrade Next.js to 16.2.4, React to 19.2.5
• Update various dependencies (algoliasearch, instantsearch.js, react-instantsearch, tinacms, @types/node, etc.)

[18-th]

/deploy

[github-actions]

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Preview URL	https://app-sswrules-staging-pr-2629.azurewebsites.net/rules
Slot Name	pr-2629
Branch	next-16-migration
Commit	1be0555dd6a8b2c04a54b0728207bb0cd815807a

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