feat: implement comprehensive database connection pooling optimization

🎯 SESSION POOLING PERFORMANCE BREAKTHROUGH!

✅ Critical Issues Fixed:
- Eliminated multiple PrismaClient instances across schedulers
- Fixed connection pool exhaustion risk in processing modules
- Implemented singleton pattern for all database connections
- Added graceful shutdown and connection cleanup

🚀 Enhanced Pooling Features:
- Dual-mode connection pooling (standard + enhanced)
- PostgreSQL native pooling with @prisma/adapter-pg
- Advanced connection monitoring and health checks
- Configurable pool limits and timeouts via environment variables
- Real-time connection statistics and metrics

📊 Performance Optimizations:
- Single shared connection pool across all schedulers
- Configurable connection limits (DATABASE_CONNECTION_LIMIT=20)
- Idle timeout management (DATABASE_POOL_TIMEOUT=10)
- Connection cycling and health validation
- Process termination signal handling

🛠️ New Infrastructure:
- lib/database-pool.ts - Advanced pooling configuration
- app/api/admin/database-health/route.ts - Connection monitoring
- Enhanced lib/prisma.ts with dual-mode support
- Comprehensive documentation in docs/database-connection-pooling.md
- Graceful shutdown handling in lib/schedulers.ts

🎛️ Environment Configuration:
- USE_ENHANCED_POOLING=true for production optimization
- DATABASE_CONNECTION_LIMIT for pool size control
- DATABASE_POOL_TIMEOUT for idle connection management
- Automatic enhanced pooling in production environments

📈 Expected Impact:
- Eliminates connection pool exhaustion under load
- Reduces memory footprint from idle connections
- Improves scheduler performance and reliability
- Enables better resource monitoring and debugging
- Supports horizontal scaling with proper connection management

Production-ready connection pooling with monitoring and health checks!

lib/database-pool.ts

@@ -0,0 +1,122 @@
+// Advanced database connection pooling configuration
+
+import { PrismaPg } from "@prisma/adapter-pg";
+import { PrismaClient } from "@prisma/client";
+import { Pool } from "pg";
+import { env } from "./env.js";
+
+// Enhanced connection pool configuration
+const createConnectionPool = () => {
+  // Parse DATABASE_URL to get connection parameters
+  const databaseUrl = new URL(env.DATABASE_URL);
+
+  const pool = new Pool({
+    host: databaseUrl.hostname,
+    port: Number.parseInt(databaseUrl.port) || 5432,
+    user: databaseUrl.username,
+    password: databaseUrl.password,
+    database: databaseUrl.pathname.slice(1), // Remove leading slash
+    ssl: databaseUrl.searchParams.get("sslmode") !== "disable",
+
+    // Connection pool configuration
+    max: env.DATABASE_CONNECTION_LIMIT, // Maximum number of connections
+    min: 2, // Minimum number of connections to maintain
+    idleTimeoutMillis: env.DATABASE_POOL_TIMEOUT * 1000, // Close idle connections after timeout
+    connectionTimeoutMillis: 10000, // Connection timeout
+    maxUses: 1000, // Maximum uses per connection before cycling
+    allowExitOnIdle: true, // Allow process to exit when all connections are idle
+
+    // Health check configuration
+    query_timeout: 30000, // Query timeout
+    keepAlive: true,
+    keepAliveInitialDelayMillis: 30000,
+  });
+
+  // Connection pool event handlers
+  pool.on("connect", (_client) => {
+    console.log(
+      `Database connection established. Active connections: ${pool.totalCount}`
+    );
+  });
+
+  pool.on("acquire", (_client) => {
+    console.log(
+      `Connection acquired from pool. Waiting: ${pool.waitingCount}, Idle: ${pool.idleCount}`
+    );
+  });
+
+  pool.on("release", (_client) => {
+    console.log(
+      `Connection released to pool. Active: ${pool.totalCount - pool.idleCount}, Idle: ${pool.idleCount}`
+    );
+  });
+
+  pool.on("error", (err) => {
+    console.error("Database pool error:", err);
+  });
+
+  pool.on("remove", (_client) => {
+    console.log(
+      `Connection removed from pool. Total connections: ${pool.totalCount}`
+    );
+  });
+
+  return pool;
+};
+
+// Create adapter with connection pool
+export const createEnhancedPrismaClient = () => {
+  const pool = createConnectionPool();
+  const adapter = new PrismaPg(pool);
+
+  return new PrismaClient({
+    adapter,
+    log:
+      process.env.NODE_ENV === "development"
+        ? ["query", "info", "warn", "error"]
+        : ["error"],
+  });
+};
+
+// Connection pool monitoring utilities
+export const getPoolStats = (pool: Pool) => {
+  return {
+    totalConnections: pool.totalCount,
+    idleConnections: pool.idleCount,
+    waitingQueries: pool.waitingCount,
+    activeConnections: pool.totalCount - pool.idleCount,
+  };
+};
+
+// Health check for the connection pool
+export const checkPoolHealth = async (
+  pool: Pool
+): Promise<{
+  healthy: boolean;
+  stats: ReturnType<typeof getPoolStats>;
+  error?: string;
+}> => {
+  try {
+    const client = await pool.connect();
+    await client.query("SELECT 1");
+    client.release();
+
+    return {
+      healthy: true,
+      stats: getPoolStats(pool),
+    };
+  } catch (error) {
+    return {
+      healthy: false,
+      stats: getPoolStats(pool),
+      error: error instanceof Error ? error.message : String(error),
+    };
+  }
+};
+
+// Graceful pool shutdown
+export const shutdownPool = async (pool: Pool) => {
+  console.log("Shutting down database connection pool...");
+  await pool.end();
+  console.log("Database connection pool shut down successfully.");
+};