Block auto-account creation when signing in via GitHub from login mode.
Signup via GitHub now shows a name confirmation dialog before redirecting
to dashboard, letting users verify/edit their display name pulled from
GitHub.
- Add intent query param to OAuth redirect, persisted in HMAC-signed state cookie
- Block registration in callback when intent=login, return no_account error
- Set wrenn_oauth_new_signup cookie on new account creation
- Frontend callback shows name confirmation dialog for new signups
- Add no_account error message to login page
Introduce pre-computed daily usage rollups from sandbox_metrics_snapshots.
An hourly background worker aggregates completed days, while today's
usage is computed live from snapshots at query time for freshness.
Backend: new daily_usage table, rollup worker, UsageService, and
GET /v1/capsules/usage endpoint with date range filtering (up to 92 days).
Frontend: replace Usage page placeholder with bar charts (Chart.js),
summary total cards, and preset/custom date range controls.
Extracts Mailer interface, EmailData, and Button to pkg/email/types.go
so the cloud repo can use them via ServerContext. internal/email re-exports
the types as aliases so existing callers are unchanged. Also fixes
pre-existing lint errors (unchecked rollback and deadline calls).
