feat: Add AI chat conversation history UI

Implemented full conversation management interface with the following features:
- Conversation history sidebar (desktop) / drawer (mobile)
- Load and display all user conversations
- Click to load specific conversation
- "New Chat" button to start fresh conversation
- Delete conversation with confirmation dialog
- Persist conversationId across messages in same conversation
- Responsive design with Material-UI breakpoints

Technical Details:
- Added Conversation interface and state management (lines 107-111)
- Load conversations from GET /api/v1/ai/conversations on mount
- Load specific conversation from GET /api/v1/ai/conversations/:id
- Delete conversation via DELETE /api/v1/ai/conversations/:id
- Updated handleSend() to pass currentConversationId instead of null
- Auto-update conversationId from API response for new conversations
- Mobile: Hamburger menu to open drawer
- Desktop: Fixed 320px sidebar with conversation list

Component grew from 420 → 663 lines

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docs/implementation-gaps.md

@@ -41,6 +41,7 @@ This document identifies features specified in the documentation that are not ye
 - ✅ **LangChain Context Management** (October 2, 2025): 4000 token budget with priority weighting, automatic context pruning
 - ✅ **Conversation Memory** (October 2, 2025): Semantic search with embeddings, conversation summarization, memory retrieval
 - ✅ **Multi-Language AI** (October 2, 2025): 5 languages (en/es/fr/pt/zh) with localized prompts and safety responses
+- ✅ **AI Chat Conversation History** (October 2, 2025): Full conversation management UI with sidebar, conversation switching, deletion, and persistence
 
 ### Key Gaps Identified
 - **Backend**: 35 features not implemented (19 completed ✅)
@@ -273,7 +274,45 @@ This document identifies features specified in the documentation that are not ye
    - Priority: Medium ✅ **COMPLETE**
    - Impact: International user support achieved
 
-5. **Prompt Injection Protection** ✅ COMPLETED (Previously)
+5. **AI Chat Conversation History UI** ✅ COMPLETED (October 2, 2025)
+   - Status: **IMPLEMENTED**
+   - Current: Full conversation management interface with sidebar, switching, and deletion
+   - Implemented:
+     * **Conversation State Management** (AIChatInterface.tsx:107-111):
+       - Tracks conversations list from API
+       - Maintains currentConversationId state
+       - Mobile drawer and delete dialog state
+     * **Load Conversations** (AIChatInterface.tsx:157-164):
+       - Fetches all user conversations on component mount
+       - Displays conversation history in sidebar/drawer
+     * **Load Conversation** (AIChatInterface.tsx:166-187):
+       - Loads specific conversation messages by ID
+       - Converts API format to Message[] format
+       - Auto-closes drawer on mobile after selection
+     * **New Conversation** (AIChatInterface.tsx:189-195):
+       - Clears current messages
+       - Resets conversationId to null for fresh chat
+     * **Delete Conversation** (AIChatInterface.tsx:197-215):
+       - Delete confirmation dialog
+       - API call to DELETE /api/v1/ai/conversations/:id
+       - Starts new conversation if deleting current one
+       - Reloads conversation list after deletion
+     * **Updated Chat Flow** (AIChatInterface.tsx:217-252):
+       - Passes currentConversationId in POST /api/v1/ai/chat
+       - Updates conversationId from API response for new chats
+       - Reloads conversation list after each message
+     * **Responsive UI**:
+       - Desktop: 320px sidebar with conversation list
+       - Mobile: Drawer with hamburger menu icon
+       - Conversation list shows title, date, delete icon
+       - Selected conversation highlighted
+       - "New Chat" button at top of sidebar
+   - Files: `maternal-web/components/features/ai-chat/AIChatInterface.tsx` (420 → 663 lines)
+   - Backend APIs Used: GET /api/v1/ai/conversations, GET /api/v1/ai/conversations/:id, DELETE /api/v1/ai/conversations/:id
+   - Priority: Medium ✅ **COMPLETE**
+   - Impact: Users can access chat history, switch conversations, and manage past conversations
+
+6. **Prompt Injection Protection** ✅ COMPLETED (Previously)
    - Status: **IMPLEMENTED**
    - Current: Comprehensive security system with 25+ regex patterns
    - Implemented: System manipulation detection, role change blocking, data exfiltration prevention, sanitizeInput() called in chat flow (ai.service.ts:193)