feat: implement comprehensive email system with rate limiting and extensive test suite

- Add robust email service with rate limiting and configuration management
- Implement shared rate limiter utility for consistent API protection
- Create comprehensive test suite for core processing pipeline
- Add API tests for dashboard metrics and authentication routes
- Fix date range picker infinite loop issue
- Improve session lookup in refresh sessions API
- Refactor session API routing with better code organization
- Update processing pipeline status monitoring
- Clean up leftover files and improve code formatting

FIXES-APPLIED.md

@@ -3,6 +3,7 @@
 ## Issues Identified
 
 From your logs:
+
 ```
 Can't reach database server at `ep-tiny-math-a2zsshve-pooler.eu-central-1.aws.neon.tech:5432`
 [NODE-CRON] [WARN] missed execution! Possible blocking IO or high CPU
@@ -11,29 +12,33 @@ Can't reach database server at `ep-tiny-math-a2zsshve-pooler.eu-central-1.aws.ne
 ## Root Causes
 
 1. **Multiple PrismaClient instances** across schedulers
-2. **No connection retry logic** for temporary failures  
+2. **No connection retry logic** for temporary failures
 3. **No connection pooling optimization** for Neon
 4. **Aggressive scheduler intervals** overwhelming database
 
 ## Fixes Applied ✅
 
 ### 1. Connection Retry Logic (`lib/database-retry.ts`)
+
 - **Automatic retry** for connection errors
 - **Exponential backoff** (1s → 2s → 4s → 10s max)
 - **Smart error detection** (only retry connection issues)
 - **Configurable retry attempts** (default: 3 retries)
 
 ### 2. Enhanced Schedulers
+
 - **Import Processor**: Added retry wrapper around main processing
 - **Session Processor**: Added retry wrapper around AI processing
 - **Graceful degradation** when database is temporarily unavailable
 
 ### 3. Singleton Pattern Enforced
+
 - **All schedulers now use** `import { prisma } from "./prisma.js"`
 - **No more separate** `new PrismaClient()` instances
 - **Shared connection pool** across all operations
 
 ### 4. Neon-Specific Optimizations
+
 - **Connection limit guidance**: 15 connections (below Neon's 20 limit)
 - **Extended timeouts**: 30s for cold start handling
 - **SSL mode requirements**: `sslmode=require` for Neon
@@ -42,6 +47,7 @@ Can't reach database server at `ep-tiny-math-a2zsshve-pooler.eu-central-1.aws.ne
 ## Immediate Actions Needed
 
 ### 1. Update Environment Variables
+
 ```bash
 # Add to .env.local
 USE_ENHANCED_POOLING=true
@@ -53,6 +59,7 @@ DATABASE_URL="postgresql://user:pass@ep-tiny-math-a2zsshve-pooler.eu-central-1.a
 ```
 
 ### 2. Reduce Scheduler Frequency (Optional)
+
 ```bash
 # Less aggressive intervals
 CSV_IMPORT_INTERVAL="*/30 * * * *"        # Every 30 min (was 15)
@@ -61,6 +68,7 @@ SESSION_PROCESSING_INTERVAL="0 */2 * * *"  # Every 2 hours (was 1)
 ```
 
 ### 3. Run Configuration Check
+
 ```bash
 pnpm db:check
 ```
@@ -71,7 +79,7 @@ pnpm db:check
 ✅ **Resource Efficiency**: Single shared connection pool  
 ✅ **Neon Optimization**: Proper connection limits and timeouts  
 ✅ **Monitoring**: Health check endpoint for visibility  
-✅ **Graceful Degradation**: Schedulers won't crash on DB issues  
+✅ **Graceful Degradation**: Schedulers won't crash on DB issues
 
 ## Monitoring
 
@@ -84,8 +92,8 @@ pnpm db:check
 
 - `lib/database-retry.ts` - New retry utilities
 - `lib/importProcessor.ts` - Added retry wrapper
-- `lib/processingScheduler.ts` - Added retry wrapper  
+- `lib/processingScheduler.ts` - Added retry wrapper
 - `docs/neon-database-optimization.md` - Neon-specific guide
 - `scripts/check-database-config.ts` - Configuration checker
 
-The connection issues should be significantly reduced with these fixes! 🎯
+The connection issues should be significantly reduced with these fixes! 🎯