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/api/l1.ts

@@ -0,0 +1,64 @@
+import { apiClient } from './client'
+import type {
+  IntakeRequest,
+  IntakeResponse,
+  QueueRow,
+  WalkSession,
+  AdhocNote,
+} from '@/types/l1'
+
+export const l1Api = {
+  intake: (body: IntakeRequest) =>
+    apiClient.post<IntakeResponse>('/l1/intake', body).then(r => r.data),
+
+  queue: (statusFilter?: string) =>
+    apiClient.get<QueueRow[]>('/l1/queue', {
+      params: statusFilter ? { status_filter: statusFilter } : {},
+    }).then(r => r.data),
+
+  listActiveSessions: () =>
+    apiClient.get<WalkSession[]>('/l1/sessions/active').then(r => r.data),
+
+  getSession: (sessionId: string) =>
+    apiClient.get<WalkSession>(`/l1/sessions/${sessionId}`).then(r => r.data),
+
+  step: (
+    sessionId: string,
+    step: { node_id: string; question: string; answer: string; note?: string | null },
+  ) =>
+    apiClient
+      .post<WalkSession>(`/l1/sessions/${sessionId}/step`, step)
+      .then(r => r.data),
+
+  notes: (sessionId: string, notes: AdhocNote[]) =>
+    apiClient
+      .post<WalkSession>(`/l1/sessions/${sessionId}/notes`, { notes })
+      .then(r => r.data),
+
+  resolve: (
+    sessionId: string,
+    body: { helpful: boolean; resolution_notes: string },
+  ) =>
+    apiClient
+      .post<WalkSession>(`/l1/sessions/${sessionId}/resolve`, body)
+      .then(r => r.data),
+
+  escalate: (
+    sessionId: string,
+    body: { reason: string; reason_category: string },
+  ) =>
+    apiClient
+      .post<WalkSession>(`/l1/sessions/${sessionId}/escalate`, body)
+      .then(r => r.data),
+
+  escalateWithoutWalk: (body: {
+    problem_statement: string
+    customer_name?: string
+    customer_contact?: string
+    reason_category: string
+    reason?: string
+  }) =>
+    apiClient
+      .post<WalkSession>('/l1/escalate-without-walk', body)
+      .then(r => r.data),
+}