In-app cards for trade updates and new messages (push tap lands on an empty Notifications)

[grunch]

Problem

Since PR-2 (#471), tapping a push opens the app on /notifications (docs/PUSH_NOTIFICATIONS.md §10: the push carries no payload, so the resync's in-app cards are meant to say what the wake was about). But nothing creates those cards today:

• NotificationsNotifier.onTradeUpdated and onNewMessage (lib/features/notifications/providers/notifications_provider.dart) are never called.
• The only producers of cards are the bond consumers in lib/core/app_bootstrap.dart (_consumeBondSlashed, _consumeBondClaims), through addIfNew.
• hydrateNotifications only reloads persisted Sembast records.

So after a trade_update push the user lands on an empty or stale screen. Raised by Codex on #471.

Scope

• Consume the trade-update stream (orders_api.onTradeUpdated, TradeUpdate { order_id, status, reason }) and the chat new-message stream in bootstrap, like the bond consumers, writing through addIfNew.
• A deterministic id so the resync's replay yields exactly one card per change (e.g. order_id + status), preserving read/delete state.
• Store stable data only; localize at render time in the 5 ARBs. The current stubs hardcode English ('Trade updated', 'New message').
• Respect the notify_trade_updates / notify_new_messages toggles.
• Delete or replace the unused onTradeUpdated / onNewMessage stubs.
• Tests: replay dedup, toggle gating, card copy per locale.

Until then the §10 promise ("tapping it opens the app on Notifications with the corresponding in-app card already present") does not hold; update the doc if the approach changes.