[FEATURE] Warn before Console API credits expire, the way subscription usage credits already do

### Preflight Checklist

- [x] I have searched [existing requests](https://github.com/anthropics/claude-code/issues?q=is%3Aissue%20label%3Aenhancement) and this feature hasn't been requested yet
- [x] This is a single feature request (not multiple features)

### Problem Statement

Console API credits expire a year after you buy them. The billing page says the
date can't be extended and expired credit isn't refundable, so the balance goes
in one go. Nothing warns you first.

Subscription usage credits do get a warning. The help centre documents an email
seven days before they expire, and those mostly don't expire at all. The credits
that do expire, on a fixed clock, get nothing.

The clock runs from purchase rather than from use, which sits badly with why
people prepay in the first place. I buy in lumps ahead of time so a long batch
doesn't stop midway for a top-up. Credit bought in January expires in January
of the following year, whether I called the API every week or not.

I searched this tracker before filing and found nothing about Console credit
expiry or a missing warning for it.

### Proposed Solution

Send the seven-day email for Console API credits as well, and a thirty-day one
if you're adding anything. The template already exists for the other balance.

Show the expiry date beside the balance in the Console too. It's in invoice
history today, which is too late to act on.

### Alternative Solutions

Count the year from last activity rather than from purchase.

Or expose the expiry date through the API and let customers handle it
themselves. That's what I ended up doing: a job that emails me sixty days out
with the balance remaining. It works, but it only knows the date because I typed
it in by hand.

### Priority

Medium - Would be very helpful

### Feature Category

API and model interactions

### Use Case Example

I bought credit for a backlog of classification work that runs in batches over
several weeks. Each top-up starts its own year, so the dates get recorded one at
a time, by hand. If I were to forget one, the balance is gone.

### Additional Context

This is billing rather than CLI behaviour. I'm filing here because the other
billing UX issues are here too, #67083 on the two balance labels and #90152 on
moving unused capacity, and the category dropdown has no billing entry.

No repository files, tests, or entry points are identified. Start by locating the existing subscription usage-credit expiry warning and its email template, then trace the Console balance display and billing data. Done means Console credits receive the proposed expiry warning and their expiry date is shown beside the balance.

Written by the indexing model from the issue text.