chore: migrate mail themes to shared framework and locked upstream inputs

framework/mail/base/header.tmpl

@@ -0,0 +1,11 @@
+<div class="framework-extra">
+{{if eq .Variant "terminal"}}<span class="email-brand">&gt; {{AppName}}</span>
+{{else if eq .Variant "mono"}}<span class="email-brand">{{AppName}}<span class="email-brand-star">*</span></span>
+{{else if eq .Variant "neon"}}<span class="email-brand">{{AppName}}</span>
+{{else if eq .Variant "heritage"}}<img src="{{AppUrl}}assets/img/favicon.png" alt="Gitea" width="40" height="40" class="email-logo" /><p class="email-brand">{{AppName}}</p>
+{{else if eq .Variant "bloom"}}<img src="{{AppUrl}}assets/img/favicon.png" alt="Gitea" width="32" height="32" class="email-logo" /><p class="email-brand">{{AppName}}</p>
+{{else if eq .Variant "ink"}}<img src="{{AppUrl}}assets/img/favicon.png" alt="Gitea" width="24" height="24" class="email-logo" /><span class="email-brand">{{AppName}}</span><br /><span class="email-tagline">Git with a cup of tea</span>
+{{else if eq .Variant "terra"}}<img src="{{AppUrl}}assets/img/favicon.png" alt="Gitea" width="28" height="28" class="email-logo" /><span class="email-brand">{{AppName}}</span><div class="email-brand-rule"></div>
+{{else if eq .Variant "aurora"}}<img src="{{AppUrl}}assets/img/favicon.png" alt="Gitea" width="24" height="24" class="email-logo" /><span class="email-brand">{{AppName}}</span>
+{{else}}<img src="{{AppUrl}}assets/img/favicon.png" alt="Gitea" width="32" height="32" class="email-logo" /><span class="email-brand">{{AppName}}</span>{{end}}
+</div>