fix: restore watermark image in email templates

The previous commit incorrectly removed the watermark — only the
style extraction into <style> blocks was requested. Restores the
watermark <img>, {{watermarkUrl}} placeholder resolution in both
EmailConnectorService and PasswordResetNotificationService, and
the corresponding test assertions.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/main/resources/email-templates/generic.html

@@ -10,7 +10,9 @@
     .wrapper { font-family:-apple-system,BlinkMacSystemFont,'Segoe UI',Roboto,sans-serif; max-width:480px; margin:0 auto; background:#fff; border-radius:8px; overflow:hidden; border:1px solid #e8e0d4; }
     .header { background:#C6820E; padding:20px 24px; text-align:center; }
     .header span { font-size:22px; font-weight:700; color:#fff; letter-spacing:0.5px; }
-    .content { padding:32px 24px 24px; }
+    .content { padding:32px 24px 24px; position:relative; overflow:hidden; }
+    .watermark { position:absolute; top:-30px; right:-50px; width:320px; height:320px; opacity:0.07; pointer-events:none; border:0; outline:none; }
+    .inner { position:relative; }
     .title { color:#1a1a1a; font-size:16px; font-weight:600; margin:0 0 8px; }
     .subtitle { color:#444; font-size:14px; line-height:1.6; margin:0 0 24px; }
     .code-box { text-align:center; margin:0 0 24px; }
@@ -30,6 +32,8 @@
       <span>Cameleer.io</span>
     </div>
     <div class="content">
+      <img src="{{watermarkUrl}}" class="watermark" alt="" />
+      <div class="inner">
       <p class="title">Quick checkpoint</p>
       <p class="subtitle">Here's your verification code. Just making sure it's really you at the reins.</p>
       <div class="code-box">
@@ -39,6 +43,7 @@
       </div>
       <p class="hint">This code expires in 10 minutes.</p>
       <p class="detail">You are receiving this email because a verification was requested on your Cameleer account. Cameleer is an observability platform for Apache Camel integrations providing real-time route tracing, message inspection, and performance monitoring. If you did not request this verification, please ignore this email or contact your administrator for assistance.</p>
+      </div>
     </div>
     <div class="footer">
       <p class="contact">Questions? Contact your administrator</p>