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/Backend/src/storage/twilio-storage.ts

@@ -111,6 +111,23 @@ export const twilioStorage = {
     });
   },
 
+  async getInternalChatSystemPrompt(userId: number): Promise<string> {
+    const settings = await db.twilioSettings.findUnique({ where: { userId } });
+    const all = (settings?.templates as Record<string, string>) || {};
+    return all["_internal_chat_system_prompt"] ?? "";
+  },
+
+  async saveInternalChatSystemPrompt(userId: number, prompt: string): Promise<void> {
+    const settings = await db.twilioSettings.findUnique({ where: { userId } });
+    const existing = (settings?.templates as Record<string, string>) || {};
+    const updated = { ...existing, "_internal_chat_system_prompt": prompt };
+    await db.twilioSettings.upsert({
+      where:  { userId },
+      update: { templates: updated },
+      create: { userId, accountSid: "", authToken: "", phoneNumber: "", templates: updated },
+    });
+  },
+
   async getRecentCommunicationsByUser(userId: number, limit = 20) {
     return db.communication.findMany({
       where: { patient: { userId } },