feat: add internal AI chat assistant and AI Input Agent page

- Add Gemini-powered internal staff chatbot (free-text input in the
  upper-right bot panel): type "check MARIA GONZALES" to search patient
  and pre-fill eligibility, or "open claims" to navigate directly
- Add /api/ai/internal-chat endpoint with LangGraph + Google Gemini
  classifier (intent: check_eligibility, find_patient, navigate_*)
- Add Users AI Chat settings section in Settings > Advanced > AI Chat
  to configure a custom system prompt for the internal assistant
- Store internal chat system prompt in existing twilioSettings JSON
  blob (no DB migration needed)
- Add AI Input Agent sidebar entry and placeholder page describing
  planned keyboard-automation typing into Open Dental / Eaglesoft

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

apps/Frontend/src/App.tsx

@@ -29,6 +29,7 @@ const ReportsPage = lazy(() => import("./pages/reports-page"));
 const CloudStoragePage = lazy(() => import("./pages/cloud-storage-page"));
 const JobMonitorPage = lazy(() => import("./pages/job-monitor-page"));
 const ChartPage = lazy(() => import("./pages/chart-page"));
+const AiInputAgentPage = lazy(() => import("./pages/ai-input-agent-page"));
 const DentalShoppingSearchTagPage = lazy(() => import("./pages/dental-shopping-search-tag-page"));
 const DentalShoppingLoginInfoPage = lazy(() => import("./pages/dental-shopping-login-info-page"));
 const ActivationPage = lazy(() => import("./pages/activation-page"));
@@ -64,6 +65,7 @@ function Router() {
       />
       <ProtectedRoute path="/reports" component={() => <ReportsPage />} />
       <ProtectedRoute path="/cloud-storage" component={() => <CloudStoragePage />} />
+      <ProtectedRoute path="/ai-input-agent" component={() => <AiInputAgentPage />} />
       <ProtectedRoute path="/dental-shopping/search-tag" component={() => <DentalShoppingSearchTagPage />} />
       <ProtectedRoute path="/dental-shopping/login-info" component={() => <DentalShoppingLoginInfoPage />} />
       <ProtectedRoute path="/activation" component={() => <ActivationPage />} adminOnly />