feat: Implement AI streaming responses with SSE and deployment infrastructure

This commit adds comprehensive AI response streaming and critical deployment features:

## AI Streaming Implementation
- **Backend StreamingService**: Token-by-token Azure OpenAI streaming (163 lines)
  - SSE endpoint at POST /api/v1/ai/chat/stream
  - Buffer management for incomplete SSE events
  - Stream callback architecture with chunk types (token, done, error)
- **Frontend useStreamingChat Hook**: Fetch API with ReadableStream (127 lines)
  - Token accumulation with state management
  - Error handling and completion callbacks
- **UI Integration**: Streaming message bubble with animated blinking cursor
  - Auto-scroll as tokens arrive
  - Loading indicator while waiting for first token
  - Seamless transition from streaming to completed message
- **Safety Integration**: All safety checks preserved
  - Rate limiting and input sanitization
  - Context building reused from chat() method

## Deployment Infrastructure (Previous Session)
- **Environment Configuration System**:
  - .env.example with 140+ configuration options
  - .env.staging and .env.production templates
  - Typed configuration service (environment.config.ts, 200 lines)
  - Environment-specific settings for DB, Redis, backups, AI
- **Secret Management**:
  - Provider abstraction for AWS Secrets Manager, HashiCorp Vault, env vars
  - 5-minute caching with automatic refresh (secrets.service.ts, 189 lines)
  - Batch secret retrieval and validation
- **Database Backup System**:
  - Automated PostgreSQL/MongoDB backups with cron scheduling
  - pg_dump + gzip compression, 30-day retention
  - S3 upload integration (backup.service.ts, 306 lines)
  - Admin endpoints for manual operations
  - Comprehensive documentation (BACKUP_STRATEGY.md, 343 lines)
- **Health Check Monitoring**:
  - Kubernetes-ready health probes (liveness/readiness/startup)
  - Custom health indicators for Redis, MongoDB, MinIO, Azure OpenAI
  - Response time tracking (health.controller.ts, 108 lines)

## Files Modified
- maternal-web/components/features/ai-chat/AIChatInterface.tsx
- maternal-app/maternal-app-backend/src/modules/ai/ai.service.ts
- maternal-app/maternal-app-backend/src/modules/ai/ai.module.ts
- docs/implementation-gaps.md (updated feature counts: 62/128 complete, 48%)

## Files Created
- maternal-web/hooks/useStreamingChat.ts

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

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

maternal-web/hooks/useStreamingChat.ts

@@ -0,0 +1,136 @@
+import { useState, useCallback } from 'react';
+import apiClient from '@/lib/api/client';
+
+export interface StreamChunk {
+  type: 'token' | 'metadata' | 'done' | 'error';
+  content?: string;
+  metadata?: any;
+  error?: string;
+}
+
+export interface ChatMessageDto {
+  message: string;
+  conversationId?: string;
+  language?: string;
+}
+
+/**
+ * Hook for streaming AI chat responses
+ * Uses Server-Sent Events (SSE) for real-time token streaming
+ */
+export function useStreamingChat() {
+  const [isStreaming, setIsStreaming] = useState(false);
+  const [error, setError] = useState<string | null>(null);
+
+  const streamMessage = useCallback(
+    async (
+      chatDto: ChatMessageDto,
+      onChunk: (chunk: StreamChunk) => void,
+      onComplete?: () => void,
+      onError?: (error: string) => void
+    ) => {
+      setIsStreaming(true);
+      setError(null);
+
+      try {
+        const response = await fetch(`${process.env.NEXT_PUBLIC_API_URL}/api/v1/ai/chat/stream`, {
+          method: 'POST',
+          headers: {
+            'Content-Type': 'application/json',
+            // Add auth token if available
+            ...(typeof window !== 'undefined' && localStorage.getItem('accessToken')
+              ? { Authorization: `Bearer ${localStorage.getItem('accessToken')}` }
+              : {}),
+          },
+          body: JSON.stringify(chatDto),
+        });
+
+        if (!response.ok) {
+          throw new Error(`HTTP error! status: ${response.status}`);
+        }
+
+        const reader = response.body?.getReader();
+        if (!reader) {
+          throw new Error('Response body is not readable');
+        }
+
+        const decoder = new TextDecoder();
+        let buffer = '';
+
+        while (true) {
+          const { done, value } = await reader.read();
+
+          if (done) {
+            break;
+          }
+
+          // Decode the chunk and add to buffer
+          buffer += decoder.decode(value, { stream: true });
+
+          // Split by newlines to process complete SSE events
+          const lines = buffer.split('\n');
+
+          // Keep the last incomplete line in the buffer
+          buffer = lines.pop() || '';
+
+          for (const line of lines) {
+            const trimmed = line.trim();
+
+            // Skip empty lines
+            if (!trimmed) {
+              continue;
+            }
+
+            // Parse SSE data format
+            if (trimmed.startsWith('data: ')) {
+              const data = trimmed.substring(6);
+
+              try {
+                const chunk: StreamChunk = JSON.parse(data);
+
+                // Emit the chunk
+                onChunk(chunk);
+
+                // Check for completion
+                if (chunk.type === 'done') {
+                  setIsStreaming(false);
+                  if (onComplete) {
+                    onComplete();
+                  }
+                  return;
+                }
+
+                // Check for errors
+                if (chunk.type === 'error') {
+                  setIsStreaming(false);
+                  const errorMsg = chunk.error || 'Streaming error occurred';
+                  setError(errorMsg);
+                  if (onError) {
+                    onError(errorMsg);
+                  }
+                  return;
+                }
+              } catch (parseError) {
+                console.error('Failed to parse SSE chunk:', parseError);
+              }
+            }
+          }
+        }
+      } catch (err) {
+        const errorMsg = err instanceof Error ? err.message : 'Streaming failed';
+        setError(errorMsg);
+        setIsStreaming(false);
+        if (onError) {
+          onError(errorMsg);
+        }
+      }
+    },
+    []
+  );
+
+  return {
+    streamMessage,
+    isStreaming,
+    error,
+  };
+}