fix: Do not generate random password on Helm upgrade

Previously, when WP_ADMIN_PASSWORD was empty, the init container would
generate a random password and update the Secret. However, Helm upgrades
would start fresh containers and regenerate a new random password, causing
the Secret to not match WordPress's actual admin password.

Changes:
- Remove random password generation logic
- Require WP_ADMIN_PASSWORD to be explicitly set in values.yaml
- Exit with error if password is not provided during installation
- Only install WordPress once when database tables don't exist
- During upgrades, no installation occurs so password remains unchanged

This ensures:
1. Initial deployment: Admin must set WP_ADMIN_PASSWORD in values.yaml
2. Helm upgrades: No password changes occur (WordPress unchanged)
3. Helm rollbacks: Original password still works
4. Secret consistency: Secret always matches WordPress's actual password

Important for users:
- Initial deployment requires WP_ADMIN_PASSWORD in values.yaml
- If not provided, installation will fail with clear error message
- This prevents the password mismatch issue on upgrades

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

templates/deployment.yaml

@@ -146,9 +146,9 @@ spec:
                 echo "=== Starting WordPress Installation ==="
 
                 if [ -z "$WP_ADMIN_PASSWORD" ]; then
-                  WP_ADMIN_PASSWORD=$(tr -dc 'A-Za-z0-9!@#$%^&*' < /dev/urandom | head -c 16)
-                  echo "Generated admin password: $WP_ADMIN_PASSWORD"
-                  echo "$WP_ADMIN_PASSWORD" > /var/www/html/wp-content/.initial-admin-password
+                  echo "ERROR: WP_ADMIN_PASSWORD is not set. WordPress installation requires an admin password."
+                  echo "Skipping WordPress installation. Please set WP_ADMIN_PASSWORD in values.yaml"
+                  exit 1
                 fi
 
                 INSTALL_URL="http://127.0.0.1"
@@ -164,9 +164,7 @@ spec:
 
                 echo "=== WordPress Installation Completed ==="
                 echo "Admin User: $WP_ADMIN_USER"
-                if [ -f /var/www/html/wp-content/.initial-admin-password ]; then
-                  echo "Admin Password: $(cat /var/www/html/wp-content/.initial-admin-password)"
-                fi
+                echo "Admin password was set from values.yaml"
               else
                 echo "WordPress is already installed, skipping installation"
                 if [ -f /tmp/wp-cli.phar ]; then