feat: explain "Failed to send" when the homeserver wants its terms accepted

A homeserver with a consent requirement (Synapse user_consent) rejects sends
with 403 M_CONSENT_NOT_GIVEN until the user accepts its current terms. The
message just showed "Failed to send" with no reason.

Listen for the SDK's HttpApiEvent.NoConsent and show a dialog naming the
user's own homeserver (the client works with any server, so no Lotus-specific
wording), with "Review and accept" opening the server's consent_uri (http(s)
only; anything else is dropped) and "I've accepted — retry sending" resending
every event that failed for this reason. "Later" snoozes it for 10 s so
background retries don't re-open it immediately.

Verified in Chromium against a local Synapse with the send endpoint answering
M_CONSENT_NOT_GIVEN: dialog shows, link opens, retry delivers the message.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PPmy3tPq869XDW4njjVaKA

src/app/pages/client/ClientNonUIFeatures.tsx

@@ -71,6 +71,7 @@ import { useTauriUpdateProgress, useTauriUpdater } from '../../hooks/useTauriUpd
 import { isNetworkUpdateError } from '../../utils/updateErrors';
 import { invokeTauri, isTauri as isTauriApp, useTauriEvent } from '../../hooks/useTauri';
 import { CloseBehaviorPrompt } from '../../components/CloseBehaviorPrompt';
+import { ConsentRequiredPrompt } from '../../components/ConsentRequiredPrompt';
 import { TauriDesktopFeatures } from '../../components/TauriDesktopFeatures';
 import { KeyboardShortcutsDialog, useKeyboardShortcutsTrigger } from '../../features/shortcuts';
 import { useRoomsListener } from '../../hooks/useRoomsListener';
@@ -1090,6 +1091,7 @@ export function ClientNonUIFeatures({ children }: ClientNonUIFeaturesProps) {
       <TauriUpdateFeature />
       <TauriDesktopFeatures />
       <CloseBehaviorPrompt />
+      <ConsentRequiredPrompt />
       <LotusDenoiseFeature />
       <DeepLinkNavigator />
       <KeyboardShortcutsFeature />