## Why
Users with several accounts at the same bank (for example a partner's
account at the same bank) need to connect the same Enable Banking ASPSP
more than once. Previously an already-connected bank was hard-blocked:
disabled in the connect dialog list, and filtered out entirely from the
onboarding inline flow with a "you already have this connected, go
reconnect" message.
## What changed
- The already-connected bank stays **selectable** and is marked with an
**"Already connected"** badge instead of being blocked/hidden.
- On the confirm step, when the selected bank already has a **live**
connection, a destructive warning explains that authorizing with the
**same bank login replaces the existing session and stops it working** —
continue only when adding a *different* account.
- The **Connect** button is gated behind an acknowledgement checkbox ("I
understand the existing connection may stop working") so a working
connection can't be replaced by accident.
- New shared `ReplaceConnectionWarning` component keeps the dialog and
inline flows from drifting apart (the same divergence #569 unified).
## Notes
- **No backend changes.** `AuthorizationController@store` already
created a fresh connection for a repeated bank; the block was
frontend-only.
- Out of scope: the previous `BankingConnection` row stays `active` in
our DB after the user re-authorizes the same login, even though Enable
Banking has invalidated it. It self-corrects on the next sync failure.
Auto-marking/cleaning the superseded connection on callback is a
separate backend follow-up.
## Testing
- New `connect-account-dialog.test.tsx`: already-connected bank is
selectable + badged, Connect is gated behind the acknowledgement, and a
fresh bank shows no warning.
- Full JS suite (234 tests) and `LocalizationTest` pass; lint and format
clean.
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