docs: fix nav logo redundancy, replace SVG with >_ prefix

The SVG icon showed "do" while the text showed "do-manager",
resulting in "do do-manager" visually. Replace with a simple
">_" prompt prefix in the nav logo.

Author: franckferman

docs/index.html

@@ -75,8 +75,7 @@
     }
     .nav-logo:hover { color: var(--text-bright); }
 
-    .nav-logo svg { flex-shrink: 0; }
-
+    .logo-prompt { color: var(--blue); margin-right: 2px; letter-spacing: -.05em; }
     .logo-do   { color: var(--blue); }
     .logo-dash { color: var(--text-dim); }
     .logo-mgr  { color: var(--text-bright); }
@@ -742,10 +741,7 @@
 <!-- ================================================================= NAV -->
 <nav>
   <a href="#top" class="nav-logo">
-    <svg width="26" height="26" viewBox="0 0 26 26" fill="none" xmlns="http://www.w3.org/2000/svg">
-      <rect width="26" height="26" rx="6" fill="#0052cc"/>
-      <text x="5" y="18" font-family="monospace" font-size="13" font-weight="700" fill="white">do</text>
-    </svg>
+    <span class="logo-prompt">&gt;_</span>
     <span><span class="logo-do">do</span><span class="logo-dash">-</span><span class="logo-mgr">manager</span></span>
   </a>