mobile: enlarge masthead logo, add breathing room, kill underline

.m-logo img grows 34px → 48px. Masthead padding 14px/18px → 28/18/26
so the logo sits with noticeably more space above and below.
text-decoration:none is now applied across :link/:visited/:hover/
:active variants (plus border-bottom:0 on both the anchor and the
<img>) to defeat any browser default underline on the tappable
logo, including Safari's quirky behaviours.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

protected/mobile/mobile.css

@@ -49,16 +49,27 @@ html, body {
   display: flex;
   justify-content: center;
   align-items: center;
-  padding: 14px 18px;
+  padding: 28px 18px 26px;
   background: var(--paper);
   border-bottom: 1px solid var(--line-soft);
 }
-.m-logo {
+.m-logo,
+.m-logo:link,
+.m-logo:visited,
+.m-logo:hover,
+.m-logo:active {
   display: inline-block;
   line-height: 0;
   text-decoration: none;
+  border-bottom: 0;
+  -webkit-tap-highlight-color: transparent;
+}
+.m-logo img {
+  height: 48px;
+  width: auto;
+  display: block;
+  border: 0;
 }
-.m-logo img { height: 34px; width: auto; display: block; }
 
 /* ─── Main layout ────────────────────────────────────────── */
 .m-main {