refactor(themes): convert all rgba() to #RRGGBBAA hex notation

453 occurrences, 37 unique rgba() values converted across 66 files.
All 110 templates (10 themes × 11 types) render successfully.

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

themes/ember/mail/repo/issue/default.tmpl

@@ -19,7 +19,7 @@
     .email-header { padding:28px 32px 16px;border-bottom:1px solid #fed7aa;background:linear-gradient(135deg,#fff7ed,#ffffff) }
 
     /* Card */
-    .email-card { max-width:600px;margin:20px auto;background:#ffffff;border-radius:16px;box-shadow:0 2px 16px rgba(234,88,12,0.08);overflow:hidden;border:1px solid #fed7aa }
+    .email-card { max-width:600px;margin:20px auto;background:#ffffff;border-radius:16px;box-shadow:0 2px 16px #ea580c14;overflow:hidden;border:1px solid #fed7aa }
     .email-text { margin:0 0 16px;font-size:16px;line-height:1.6;color:#78350f }
 
     /* Content */