docs: draft ten logo concepts

Eight fresh directions plus two refinements of the shipped mark, each
authored as a real currentColor SVG in the app's house style rather than
as a description, so any of them can be dropped straight in and the
favicon tile is a mechanical derivation.

Every mark was rendered at 120/32/24/16px and looked at, which changed
the set three times: the braid came out as a plain multiplication sign
and was rebuilt with actual over/under crossings, the anchor was
rebalanced to three-fold symmetry, and the first return-arc read even
more like a copyright glyph than the current one.

The finding that matters is not one of the eight. The mark shipping
today fails at 16px — its outer strokes drop out to rasterisation and
the 2.5px gap to the node fills in, so the favicon renders as a smear.
Concept 09 fixes that in five lines and is worth taking regardless of
whether anything here replaces the mark.

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

docs/logo-concepts/06-spine.svg

@@ -0,0 +1,11 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 64 64" width="64" height="64" role="img" aria-label="Spine">
+  <title>Spine</title>
+  <!-- An index: many entries on one shared spine, the active one reaching furthest. -->
+  <g fill="none" stroke="currentColor" stroke-width="6" stroke-linecap="round">
+    <path d="M16 13V51"/>
+    <path d="M16 21H34" opacity=".5"/>
+    <path d="M16 32H42"/>
+    <path d="M16 43H34" opacity=".5"/>
+  </g>
+  <circle cx="52" cy="32" r="5" fill="currentColor"/>
+</svg>