feat: add PostgreSQL initialization script for AI stack

Created database initialization script following the core stack pattern.
The script automatically creates required databases on first initialization:
- openwebui: Open WebUI application database
- litellm: LiteLLM proxy database for API key management and tracking

Changes:
- Created ai/postgres/init/01-init-databases.sh
- Mounted init directory in ai_postgres service
- Added automatic privilege grants to AI_DB_USER

Note: Init script only runs on first database creation when volume is empty.

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

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

ai/compose.yaml

@@ -13,6 +13,7 @@ services:
       POSTGRES_INITDB_ARGS: --auth-host=scram-sha-256
     volumes:
       - ai_postgres_data:/var/lib/postgresql/data
+      - ./postgres/init:/docker-entrypoint-initdb.d
     healthcheck:
       test: ["CMD-SHELL", "pg_isready -U ${AI_DB_USER}"]
       interval: 30s

ai/postgres/init/01-init-databases.sh

@@ -0,0 +1,38 @@
+#!/bin/bash
+set -e
+
+# PostgreSQL initialization script for AI stack
+# This script runs on first database initialization
+# Creates all databases required by AI services
+
+echo "Starting AI stack database initialization..."
+
+psql -v ON_ERROR_STOP=1 --username "$POSTGRES_USER" --dbname "$POSTGRES_DB" <<-EOSQL
+    -- Create databases for AI services
+    -- Open WebUI database
+    SELECT 'CREATE DATABASE openwebui'
+    WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'openwebui')\gexec
+
+    -- LiteLLM proxy database
+    SELECT 'CREATE DATABASE litellm'
+    WHERE NOT EXISTS (SELECT FROM pg_database WHERE datname = 'litellm')\gexec
+
+    -- Grant privileges to all databases
+    GRANT ALL PRIVILEGES ON DATABASE openwebui TO $POSTGRES_USER;
+    GRANT ALL PRIVILEGES ON DATABASE litellm TO $POSTGRES_USER;
+
+    -- Log success
+    SELECT 'AI stack databases initialized:' AS status;
+    SELECT datname FROM pg_database
+    WHERE datname IN ('openwebui', 'litellm')
+    ORDER BY datname;
+EOSQL
+
+echo ""
+echo "✓ PostgreSQL initialization completed"
+echo "✓ All AI stack databases created successfully"
+echo ""
+echo "Databases available:"
+echo "  • openwebui    - Open WebUI application database"
+echo "  • litellm      - LiteLLM proxy database"
+echo ""