`ng add @angular/fire` stops with `Cannot read properties of undefined (reading 'email')` on firebase-tools 15

Start with src/schematics/setup/prompts.ts:110 and src/schematics/setup/index.ts:95, then inspect src/schematics/firebaseTools.ts:30 and reproduce with firebase-tools 15. Add coverage for the version 15 login shape and ensure setup proceeds through the account, project and app questions without writing errors.

ng add @angular/fire fails for anyone whose Firebase CLI is version 15, which is what npm installs today.

Reproduction

In an Angular 21 application with firebase-tools 15.28.1 resolvable, run ng add @angular/fire@next and pick any feature. Setup prints:

Using firebase-tools version 15.28.1
Cannot read properties of undefined (reading 'email')

It stops there, before the account, project and app questions, so nothing is written to the workspace.

Cause

userPrompt in src/schematics/setup/prompts.ts:110 reads defaultUser.email, where defaultUser comes from await firebaseTools.login(options).

• Called inside a terminal, that call returns an object carrying email on firebase-tools 14.27.0 and returns undefined on 15.28.1, so the read throws.
• src/schematics/setup/index.ts:95 reads user.email from the same source and has the same exposure.

Who hits it

Everyone with firebase-tools 15 installed, and everyone with no Firebase CLI at all:

• src/schematics/firebaseTools.ts:30 installs the newest version (npm i --location=global firebase-tools), which is 15.30.2 today.
• The declared range accepts it (firebase-tools: ^14.0.0 || ^15.0.0, widened in #3701).
• Installing firebase-tools 14 makes the whole flow complete.

Directions for a fix

Read the account from login.list() rather than from login(), or treat an undefined return as "no default account" instead of reading a property from it. A spec covering the version 15 shape would be worth adding, since nothing exercises this path today.