Move dashboard settings into Y3R C4LL tab, drop standalone S3TT1NGS page

mara (issue #3817): remove the home link + page, put the setting toggle into the Y3R C4LL tab. Deleted settings.html/.js/.css; the browser-notification toggle (the only content there) now renders as a ◆ PR3F3R3NC3S ◆ section under Y3R C4LL's approvals/inbox, wired the same way (NOTIF.bind()/NOTIF.show() in common.js — no behavior change, just a new mount point). Updated build.mjs's entry lists and every doc/comment that pointed at the old page.

docs/web-ui/README.md

@@ -26,11 +26,12 @@ of your time. It's a single page with exactly four tabs:
 Everything else lives on its own page instead, all reachable from the
 H0M3 hub: **Flow** (`/flow.html`, the raw live message stream across
 the whole swarm), **Logs** (`/logs.html`, per-agent and host
-journals), **Stats** (`/stats.html`, swarm-wide usage stats), **Settings**
-(`/settings.html`, your local browser preferences), **Builds** (`/builds.html`, the rebuild
-queue and build history), **Core** (`/core.html`, tombstones and
-container resource use), and **Credentials** (`/credentials.html`,
-provisioning matrix/GitHub/forge accounts per agent).
+journals), **Stats** (`/stats.html`, swarm-wide usage stats),
+**Builds** (`/builds.html`, the rebuild queue and build history),
+**Core** (`/core.html`, tombstones and container resource use), and
+**Credentials** (`/credentials.html`, provisioning matrix/GitHub/forge
+accounts per agent). Your local browser preferences (notifications)
+live in the dashboard's Y3R C4LL tab now, not a separate page.
 
 Each agent also has its own page — a full terminal view of that
 agent's session, reachable by clicking its name anywhere in the