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/settings.ts

@@ -226,7 +226,7 @@ interface SettingsView {
   open: () => void;
 }
 
-export function settingsMain(board: HTMLElement, views: { hide: () => void }[]): SettingsView {
+export function settingsMain(views: { hide: () => void }[], goHome: () => void): SettingsView {
   const view = must<HTMLElement>("#settings");
   const deck = must<HTMLElement>("#deck");
   const nav = must<HTMLButtonElement>("#nav-settings");
@@ -705,7 +705,6 @@ export function settingsMain(board: HTMLElement, views: { hide: () => void }[]):
     for (const sibling of views) {
       sibling.hide();
     }
-    board.hidden = true;
     deck.hidden = true;
     view.hidden = false;
     nav.setAttribute("aria-pressed", "true");
@@ -720,7 +719,7 @@ export function settingsMain(board: HTMLElement, views: { hide: () => void }[]):
 
   function close() {
     hide();
-    board.hidden = false;
+    goHome();
     nav.focus();
   }
 
@@ -729,7 +728,7 @@ export function settingsMain(board: HTMLElement, views: { hide: () => void }[]):
       navigate({ kind: "settings" });
       open();
     } else {
-      navigate({ kind: "board" });
+      navigate({ kind: "library" });
       close();
     }
   });
@@ -748,7 +747,7 @@ export function settingsMain(board: HTMLElement, views: { hide: () => void }[]):
     (event) => {
       if (event.key === "Escape" && !view.hidden) {
         event.stopImmediatePropagation();
-        navigate({ kind: "board" });
+        navigate({ kind: "library" });
         close();
       }
     },