feat(ui): HostedAiBanner one-time hosted-AI notice component (T10.3/M3.3)

New component mirroring ConsentNotice.svelte's card/overlay pattern:
shown before first use of a hosted (non-local) provider, explains that
the transcript leaves the device to a third party, and offers
accept/cancel. Uses the existing design tokens (--accent, --warning,
--bg-elevated, --radius-lg/sm, --shadow-lg) so it matches the
recording-consent notice visually. Not yet wired into any view — next
commits add it to Settings and SummaryPanel.

src/lib/components/HostedAiBanner.svelte

@@ -0,0 +1,94 @@
+<script lang="ts">
+  // One-time third-party "data leaves your device" notice (ADR-0011, T10.3/
+  // M3.3), shown before the first use of any hosted (non-local) AI provider —
+  // Anthropic today, a hosted OpenAI-compatible gateway once wired the same
+  // way. Same shared-copy/shared-acknowledgment pattern as ConsentNotice.svelte
+  // (recording consent, ADR-0009): both gate a single Settings toggle AND a
+  // second use-time trigger point on the same one-time flag.
+  import { Globe } from "@lucide/svelte";
+  let {
+    providerLabel,
+    onAccept,
+    onCancel,
+  }: { providerLabel: string; onAccept: () => void; onCancel: () => void } = $props();
+</script>
+
+<div class="banner" role="alertdialog" aria-labelledby="hosted-ai-heading">
+  <div class="heading">
+    <Globe size={18} aria-hidden="true" />
+    <strong id="hosted-ai-heading">Before using {providerLabel}</strong>
+  </div>
+  <p>
+    Generating with <strong>{providerLabel}</strong> sends this meeting's transcript to their
+    servers — it leaves this device and is subject to their privacy policy. WhispAssist has no
+    control over data handling once it leaves your device. This is off by default; you're choosing
+    it now.
+  </p>
+  <div class="actions">
+    <button class="primary" onclick={onAccept}>I understand — continue</button>
+    <button class="ghost" onclick={onCancel}>Cancel</button>
+  </div>
+</div>
+
+<style>
+  .banner {
+    border: 1px solid var(--border);
+    border-radius: var(--radius-lg);
+    box-shadow: var(--shadow-lg);
+    padding: 1rem 1.1rem;
+    background: var(--bg-elevated);
+    color: var(--fg);
+    max-width: 420px;
+  }
+  .heading {
+    display: flex;
+    align-items: center;
+    gap: 0.45rem;
+    color: var(--warning);
+    margin-bottom: 0.4rem;
+  }
+  .heading strong {
+    color: var(--fg);
+  }
+  p {
+    margin: 0;
+    font-size: 0.9rem;
+    line-height: 1.5;
+    color: var(--muted);
+  }
+  p strong {
+    color: var(--fg);
+  }
+  .actions {
+    display: flex;
+    align-items: center;
+    gap: 0.6rem;
+    flex-wrap: wrap;
+    margin-top: 0.8rem;
+  }
+  button {
+    font: inherit;
+    cursor: pointer;
+  }
+  button.primary {
+    background: var(--accent);
+    color: var(--accent-fg);
+    border: 1px solid transparent;
+    padding: 0.4rem 0.8rem;
+    border-radius: var(--radius-sm);
+    font-weight: 600;
+  }
+  button.primary:hover {
+    background: var(--accent-hover);
+  }
+  button.ghost {
+    background: none;
+    border: 1px solid var(--border);
+    padding: 0.4rem 0.8rem;
+    border-radius: var(--radius-sm);
+    color: var(--fg);
+  }
+  button.ghost:hover {
+    background: var(--bg-hover);
+  }
+</style>