feat(web): library homepage, chain in settings

Implements the §9.7 shell rulings (issue #173): "/" renders the library
and the board route is gone — every former board target (Esc, cleared
search, detail parent routes, the not-found fallback) lands on the
library. The signal chain moves into /settings as its first section,
lamps still driven by the health poll; the master lamp stays on the
rail. The wordmark is now a real anchor that navigates home.

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

web/src/style.css

@@ -156,6 +156,8 @@ body {
   gap: var(--space-3);
 }
 
+/* §9.7: the wordmark is a link home — quiet at rest, cyan on approach
+   like every other interactive control */
 .wordmark {
   margin: 0;
   font-family: var(--font-display);
@@ -163,6 +165,13 @@ body {
   font-weight: 700;
   letter-spacing: 0.1em;
   line-height: 1;
+  color: var(--ink);
+  text-decoration: none;
+}
+
+.wordmark:hover,
+.wordmark:focus-visible {
+  color: var(--accent-bright);
 }
 
 .rail-meta {
@@ -247,44 +256,26 @@ body {
   }
 }
 
-.board.powered .lamp {
+.chain.powered .lamp {
   animation: lamp-strike 420ms var(--ease-out) both;
   animation-delay: calc(var(--strike, 0) * 120ms);
 }
 
-.board.powered .lamp[data-state="off"] {
+.chain.powered .lamp[data-state="off"] {
   animation: none;
 }
 
 @media (prefers-reduced-motion: reduce) {
   .lamp[data-state="probing"],
-  .board.powered .lamp {
+  .chain.powered .lamp {
     animation: none;
   }
 }
 
-/* ---- board and chain ------------------------------------------------- */
-
-.board {
-  width: 100%;
-  max-width: 68rem;
-  margin: 0 auto;
-  padding: var(--space-12) var(--space-6);
-  flex: 1;
-  display: flex;
-  align-items: center;
-}
-
-/* the deck swaps in over the board; flex would beat [hidden] otherwise */
-.board[hidden] {
-  display: none;
-}
+/* ---- signal chain (§9.7: a settings section, no route of its own) ----- */
 
 .chain {
   width: 100%;
-}
-
-.chain {
   display: grid;
   grid-template-columns: 1fr 2.5rem 1.2fr 2.5rem 1fr;
   grid-template-areas:
@@ -1811,10 +1802,6 @@ body {
     flex: 1;
   }
 
-  .board {
-    padding: var(--space-6) var(--space-4);
-  }
-
   .chain {
     grid-template-columns: 1fr;
     grid-template-areas: