feat: add password reset security notification email endpoint

Adds POST /api/password-reset-notification (public, rate-limited 3/10min)
that sends a branded HTML security notification email via the runtime-
configured Logto SMTP connector. Uses spring-boot-starter-mail with a
programmatic JavaMailSender built from the connector's live credentials.

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

pom.xml

@@ -100,6 +100,12 @@
             <version>3.4.1</version>
         </dependency>
 
+        <!-- Mail (for password-reset security notification) -->
+        <dependency>
+            <groupId>org.springframework.boot</groupId>
+            <artifactId>spring-boot-starter-mail</artifactId>
+        </dependency>
+
         <!-- Test -->
         <dependency>
             <groupId>org.springframework.boot</groupId>