Retire the Dashboard tab; Processes is the front page

The app repeated itself. The module list, /api/prefs/dashboard, applyPrefs and the
per-user dashboard blob are gone. Widgets stays and now says plainly that it is for
dashboards outside Ham Lab.

This also closes a bug: applyPrefs set the sampling rate from intervalMs inside the
dashboard layout, and reset it to the default when that field was absent — so with
per-user layouts, one account saving a dashboard could reset the sampling rate for the
whole machine. The sampler now has one source.

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

web/src/Gallery.tsx

@@ -57,6 +57,13 @@ export default function Gallery() {
 
   return (
     <div className="dash gallery">
+      <div className="notice" style={{ marginBottom: 10 }}>
+        These widgets are for <b>dashboards outside Ham Lab</b> — Glance, Home Assistant, a wall
+        display. Each one is a page at <span className="mono">/embed/widget</span> you put in an
+        iframe, reading this machine through a <b>read-only sensor token</b> (Settings → Access
+        tokens). Ham Lab shows you these numbers on its own pages; this tab is for handing them
+        to something else.
+      </div>
       <div className="dash-bar">
         <span className="hint">{needle ? `${shown.length} of ${sensors.length}` : sensors.length} sensors on this machine · live · tap a tile to copy its ID</span>
         <input className="gallery-find" value={find} onChange={(e) => setFind(e.target.value)} placeholder="find — gitea, temp, enp3s0…" spellCheck={false} autoCapitalize="off" />