feat: add TenantConnectionManager with dynamic pool management

- Adds pg dependency for direct PostgreSQL connections to tenant DBs
- TenantConnectionManager: singleton managing Map<tenantId, Pool>
- provisionDatabase: creates new DB with tables and indexes
- deprovisionDatabase: soft-deletes by renaming DB
- Automatic idle pool cleanup every 60s (5min threshold)
- Max 3 connections per pool (6/tenant with 2 PM2 workers)
- Graceful shutdown support for all pools

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

pnpm-lock.yaml

@@ -68,6 +68,9 @@ importers:
       node-forge:
         specifier: ^1.3.3
         version: 1.3.3
+      pg:
+        specifier: ^8.18.0
+        version: 8.18.0
       zod:
         specifier: ^3.23.0
         version: 3.25.76
@@ -96,6 +99,9 @@ importers:
       '@types/node-forge':
         specifier: ^1.3.14
         version: 1.3.14
+      '@types/pg':
+        specifier: ^8.18.0
+        version: 8.18.0
       prisma:
         specifier: ^5.22.0
         version: 5.22.0
@@ -1106,6 +1112,9 @@ packages:
   '@types/pako@2.0.4':
     resolution: {integrity: sha512-VWDCbrLeVXJM9fihYodcLiIv0ku+AlOa/TQ1SvYOaBuyrSKgEcro95LJyIsJ4vSo6BXIxOKxiJAat04CmST9Fw==}
 
+  '@types/pg@8.18.0':
+    resolution: {integrity: sha512-gT+oueVQkqnj6ajGJXblFR4iavIXWsGAFCk3dP4Kki5+a9R4NMt0JARdk6s8cUKcfUoqP5dAtDSLU8xYUTFV+Q==}
+
   '@types/prop-types@15.7.15':
     resolution: {integrity: sha512-F6bEyamV9jKGAFBEmlQnesRPGOQqS2+Uwi0Em15xenOxHaf2hv6L8YCVn3rPdPJOiJfPiCnLIRyvwVaqMY3MIw==}
 
@@ -3369,6 +3378,12 @@ snapshots:
 
   '@types/pako@2.0.4': {}
 
+  '@types/pg@8.18.0':
+    dependencies:
+      '@types/node': 22.19.7
+      pg-protocol: 1.11.0
+      pg-types: 2.2.0
+
   '@types/prop-types@15.7.15': {}
 
   '@types/qs@6.14.0': {}