feat: add the logo, and point people at the plugin before they mint a token

Logo: the app had no icon at all — public/ held only .gitkeep and the page
emitted no <link rel="icon">, so browsers requested /favicon.ico, got a 404
and showed a blank tab. app/icon.svg is picked up automatically by the App
Router; public/logo.svg is a currentColor variant for in-app use.

The mark is three retrieval signals converging on a single memory, which is
what the search actually does (vector + full-text + tags fused by RRF) and
what the product does (many sessions, one store). Checked at 16px: the outer
strokes are held at equal opacity because asymmetry read as a rendering
artifact rather than as ranking.

Tokens page: reframed so a bearer token is the exception rather than the
default. A token is a credential to store and rotate; the plugin just signs
you in. The install hint renders only when PLUGIN_MARKETPLACE_URL is set —
a copyable command pointing nowhere is worse than no command.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

apps/web/public/logo.svg

@@ -0,0 +1,14 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" width="64" height="64" role="img" aria-label="shared-memory">
+  <title>shared-memory</title>
+  <!--
+    Transparent, currentColor variant of the mark for in-app use - inherits
+    the surrounding text color so it works on any surface. The tile version
+    used as the favicon lives at app/icon.svg.
+  -->
+  <g fill="none" stroke="currentColor" stroke-linecap="round" stroke-width="7">
+    <path d="M13 15C25 15 27 32 37 32" opacity=".45"/>
+    <path d="M13 32H37"/>
+    <path d="M13 49C25 49 27 32 37 32" opacity=".7"/>
+  </g>
+  <circle cx="43" cy="32" r="8" fill="currentColor"/>
+</svg>