fix(templates): add inline colors for dark-background themes, set CanReply=false

- aurora, neon, terminal: add explicit inline color styles to bare
  text elements (locale.Tr calls, h4 headings, download labels)
  that were invisible in clients stripping <style> blocks (Gmail).
  33 files across 3 dark-background themes.
- CanReply: changed from true to false in mock data — matches
  typical Gitea deployment where IncomingEmail is disabled by
  default. Template syntax kept identical to official Gitea.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

themes/neon/mail/user/auth/activate_email.tmpl

@@ -36,7 +36,7 @@
           <a href="{{$activate_url}}" class="resp-btn" style="display:inline-block;padding:13px 36px;font-size:14px;font-weight:700;color:#0a0a0f;text-decoration:none;background:linear-gradient(135deg,#ff2d95,#e0115f);border:1px solid #ff2d95;box-shadow:0 0 16px rgba(255,45,149,0.4);letter-spacing:1px;text-transform:uppercase;">Verify Email Address</a>
         </td></tr></table>
         <table width="100%" cellpadding="0" cellspacing="0" border="0" style="border:1px solid rgba(0,212,255,0.2);background:rgba(0,212,255,0.04);"><tr><td style="padding:14px 16px;">
-          <p style="margin:0 0 6px;font-size:12px;color:#00d4ff;">{{.locale.Tr "mail.link_not_working_do_paste"}}</p>
+          <p style="margin:0 0 6px;font-size:12px;color:#00d4ff;"><span style="color:#64748b;">{{.locale.Tr "mail.link_not_working_do_paste"}}</span></p>
           <p style="margin:0;font-size:11px;font-family:monospace;color:#00d4ff;background:rgba(0,0,0,0.3);padding:8px 10px;border:1px solid rgba(0,212,255,0.15);word-break:break-all;">{{$activate_url}}</p>
         </td></tr></table>
       </td></tr>