Modernize functions/ to Firebase v2 SDK, Node ≥22; remove node-fetch from root lib

[Copilot]

The functions/ sub-project was pinned to an EOL stack (Node 16, firebase-admin@^11, firebase-functions@^4, ESLint 8 + eslint-config-google) while the root library had already moved to v2/Node 22. It also relied on a Gen-1 Auth trigger with no direct Gen-2 equivalent, and the root library depended on node-fetch with a timeout option that is silently ignored on node-fetch@3.

Auth trigger migration

• Replaced the Gen-1 functions.runWith().auth.user().onCreate() trigger with the Gen-2 blocking function beforeUserCreated (firebase-functions/v2/identity), dropping the @ts-ignore in favor of an explicit typed cast:

export const created = beforeUserCreated({
  memory: '512MiB',
  timeoutSeconds: 60,
}, async (event) => {
  const user = event.data;
  if (!user) return;
  await User.Helper.onCreate(user as unknown as UserRecord, mainUrl);
});

• Replaced remaining @ts-ignore in actions.ts with typed catch (error: any) narrowing.

functions/ dependency & tooling upgrade

• engines.node → >=22, firebase-admin → ^13, firebase-functions → ^7, typescript → ^6.
• Removed unused cors, @google-cloud/functions-framework, firebase-functions-test.
• Replaced legacy .eslintrc.json/.eslintignore with a flat eslint.config.js mirroring the root config; dropped the unmaintained eslint-config-google/ESLint 8 toolchain.
• Fixed tsconfig.json's module/moduleResolution mismatch and removed unused experimentalDecorators, emitDecoratorMetadata, downlevelIteration, and other deprecated compiler options.
• Fixing the tsconfig let the project compile for the first time in a while, which surfaced a real bug in media/open.ts: a required request field was missing from the Media.Helper.preview call — now passed through.

Root library: drop node-fetch

• src/api-request.ts and src/media.ts now use native fetch (Node ≥22) instead of node-fetch, replacing the ignored timeout option with AbortSignal.timeout(60000) and dropping node-fetch-only options (follow, size, agent, compress).
• Removed the node-fetch dependency and updated tests to mock the global fetch.
• Removed unused experimentalDecorators/emitDecoratorMetadata from the root tsconfig.json.

Docs

• Updated README.MD / functions/README.MD to reflect the new Node/SDK versions and the v1→v2 trigger change.

Out of scope

• Repo-wide strictNullChecks/noImplicitAny re-enablement was not attempted — it surfaces ~30 unrelated null-safety diagnostics across user.ts, media.ts, global.ts, etc., and warrants a dedicated follow-up.
• express stays at ^4 in functions/; bumping to ^5 changes wildcard route matching (/media/**) and needs its own review. @types/express was aligned to ^5 (dev-only) to match the compiled root library types.