fix(antigravity): label quota rows by group and move the prose to meta

[kittors]

Backend half of showing both Antigravity quota windows the way the upstream client does. Pairs with codeProxy — merge this first, see below.

The problem

The row label joined the group name to the upstream's bucket wording:

Gemini Models · Weekly Limit Remaining

Too long for a card row, and being upstream prose it could not be localised — the card showed an English sentence where every other provider shows a short localised label.

The change

• Label carries the group name alone. The window is already in WindowSeconds, so the card can render it in the operator's language and compose <group> · <window> itself.
• The upstream's description moves into Meta, joined with the bucket's own description when the two differ. The card puts it behind a hint icon instead of printing it, so a full sentence cannot crowd out the numbers.

Nothing here decides presentation: the group name and both descriptions are the upstream's own strings, and the window is a duration rather than a phrase.

Merge order

New backend + old panel would render two rows both labelled "Gemini Models" with nothing to tell them apart. Old backend + new panel degrades safely — the rows keep their existing labels and simply do not group.

So: merge this, then the codeProxy PR. Both deploy in minutes, and the intermediate state is only reachable in the gap between them.

Verification

go build ./... and gofmt clean; full go test ./... green. New test pins that every row in a group is labelled with the group name alone, and that a bucket describing itself contributes to the hint alongside the group description.

Still not verifiable against production: the host has no antigravity accounts (ai_account_status holds only xai, codex and claude).

🤖 Generated with Claude Code