feat(quota): read Claude plan limits from the Claude Code login

Claude quota only worked when the user had signed into Anthropic through
OpenCode. Credentials are now discovered from Claude Code itself first: the
macOS Keychain entry, then the Linux/WSL credentials file (honouring
CLAUDE_CONFIG_DIR), then OpenCode auth.json, then CLAUDE_CODE_OAUTH_TOKEN.

All sources stay read-only and the OAuth token is never refreshed: Anthropic
allows one live refresh token per client_id, so refreshing here would sign the
user out of Claude Code. Credentials are re-read per request instead, and an
expired token reports that Claude Code needs a sign-in rather than a bare 401.

Usage is now read from the limits[] array, so model-scoped weekly limits work
again after Anthropic stopped populating seven_day_sonnet/seven_day_opus, and
new limit kinds no longer need a code change. Adds extra-usage spend and the
plan name, and holds the last good values through Anthropic's 429s with a
cooldown and an account-keyed cache.

packages/ui/src/components/sections/usage/UsagePage.tsx

@@ -162,6 +162,11 @@ export const UsagePage: React.FC = () => {
       description={
         isLoading ? (
           <span className="animate-pulse typography-settings-description text-muted-foreground">{t('settings.usage.page.header.refreshing')}</span>
+        ) : selectedResult?.planLabel ? (
+          t('settings.usage.page.header.lastUpdatedWithPlan', {
+            plan: selectedResult.planLabel,
+            time: formatTime(lastUpdated, timeFormatPreference),
+          })
         ) : (
           t('settings.usage.page.header.lastUpdated', { time: formatTime(lastUpdated, timeFormatPreference) })
         )