feat(ui): brand mark logo in the web UI, panel, and favicon

The mark is the same drawing in three places with three different
colour sources: /static/logo.svg carries a fixed palette because a
favicon has no page to inherit from, the {{define "mark"}} block takes
--ink/--ember so it flips with the theme, and the userscript copy lives
inside the shadow root next to the tokens it uses.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

userscript/manga-bookmark.user.js

@@ -1383,7 +1383,31 @@
     <div id="backdrop"></div>
     <aside id="panel" role="dialog" aria-label="Manga bookmarks">
       <header>
-        <span>manga<em>Bookmark</em></span>
+        <span class="brand">
+          <svg class="mark" viewBox="0 0 200 172" aria-hidden="true">
+            <g fill="var(--ink)" stroke="currentColor" stroke-width="6.5" stroke-linejoin="round" stroke-linecap="round">
+              <path fill="none" d="M28 36H4v114h192V36h-24"></path>
+              <path fill="none" d="M28 23H17v127h166V23h-11"></path>
+              <g id="mb-half">
+                <path d="M28 7 88 55v97L28 138z"></path>
+                <g fill="currentColor" stroke="none">
+                  <path d="M37 25 55 39v41L37 66z"></path>
+                  <path d="M60 42 79 57v42L60 84z"></path>
+                  <path d="M37 75 79 108v13L37 88z"></path>
+                  <path d="M37 98 79 129v11L37 131z"></path>
+                </g>
+              </g>
+              <use href="#mb-half" transform="matrix(-1 0 0 1 200 0)"></use>
+              <g stroke="var(--ember)">
+                <path d="M100 4l9 5v11l-9 5-9-5V9z"></path>
+                <path d="M94 24h12v24H94z"></path>
+                <path d="M70 47h60v14H70z"></path>
+                <path d="M91 61h18v87l-9 20-9-20z"></path>
+              </g>
+            </g>
+          </svg>
+          <span>manga<em>Bookmark</em></span>
+        </span>
         <button id="closeBtn" aria-label="Close">close</button>
       </header>
       <div id="nav">
@@ -1458,11 +1482,15 @@
     }
     #panel.open { transform: translateX(0); }
     header {
-      display: flex; align-items: baseline; justify-content: space-between;
+      display: flex; align-items: center; justify-content: space-between;
       padding: 16px; border-bottom: 1px solid var(--rule);
       font: 400 22px/1 var(--font-display); color: var(--paper);
     }
     header em { color: var(--ember); font-style: italic; }
+    .brand { display: flex; align-items: center; gap: 9px; }
+    /* 5px stroke on a 200-unit grid thins out at this size: the markup carries
+       6.5 instead. overflow visible keeps the topmost blade pip from clipping. */
+    .mark { width: 26px; height: 22px; flex: none; overflow: visible; }
     #closeBtn {
       background: none; border: none; color: var(--mute); cursor: pointer;
       font: 500 10px var(--font-mono); letter-spacing: .12em; text-transform: uppercase;