feat(l1): real L1 dashboard with empty-state + resume widget

Replaces the T20 stub. L1 dashboard renders greeting, "Describe the
problem" intake card (autofocus textarea, optional customer fields,
primary "Start walk" CTA), open-tickets queue (Phase 1: display-only),
and a "Resume in progress" widget listing the L1's active sessions
ordered by last_step_at DESC. Empty-state card shows on accounts with
no queue + no active sessions (first-run nudge to upload KB or auth flows).

Adds /api/l1.ts (full L1 API client surface) and /types/l1.ts.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/components/l1/EmptyStateCard.tsx

@@ -0,0 +1,35 @@
+import { usePermissions } from '@/hooks/usePermissions'
+
+interface Props {
+  onUploadClick?: () => void
+}
+
+export function EmptyStateCard({ onUploadClick }: Props) {
+  const { canCoverL1 } = usePermissions()
+
+  return (
+    <div className="rounded-lg border border-default bg-card p-6">
+      <h2 className="font-heading text-xl font-bold text-heading mb-2">
+        Your knowledge base is empty
+      </h2>
+      <p className="text-muted-foreground mb-4">
+        L1 Workspace works best when your account has KB content or authored flows.
+        Right now there's nothing to match against — calls will start as ad-hoc walks.
+      </p>
+      {canCoverL1 && onUploadClick ? (
+        <button
+          type="button"
+          onClick={onUploadClick}
+          className="rounded-md bg-accent text-white px-4 py-2 text-sm font-medium hover:bg-accent/90 transition-colors"
+        >
+          Upload KB content
+        </button>
+      ) : (
+        <ul className="text-sm text-muted-foreground space-y-1 ml-4 list-disc">
+          <li>Ask your admin to upload KB documents</li>
+          <li>Or ask them to author a flow in the Flows library</li>
+        </ul>
+      )}
+    </div>
+  )
+}