refactor: every count in the web app is said by one plural(), with the viewer's thousands separator; a source guard names any hand-written copy (M505 #5642)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web/src/lib/components/ActiveSessions.svelte

@@ -1,4 +1,5 @@
 <script lang="ts">
+  import { plural } from '#lib/utils/plural.js';
   import { onMount } from 'svelte';
   import { MonitorSmartphone, TriangleAlert } from 'lucide-svelte';
   import {
@@ -55,7 +56,7 @@
     busy = true;
     try {
       const n = await revokeOtherSessions();
-      pushToast(n === 1 ? 'Signed out 1 other device.' : `Signed out ${n} other devices.`);
+      pushToast(`Signed out ${plural(n, 'other device', 'other devices')}.`);
       confirmingLogoutOthers = false;
       await load();
     } catch {
@@ -101,7 +102,7 @@
     if (mins < 1) return 'just now';
     if (mins < 60) return `${mins} min ago`;
     const hours = Math.round(mins / 60);
-    if (hours < 24) return hours === 1 ? '1 hour ago' : `${hours} hours ago`;
+    if (hours < 24) return `${plural(hours, 'hour', 'hours')} ago`;
     const days = Math.round(hours / 24);
     if (days < 30) return days === 1 ? 'yesterday' : `${days} days ago`;
     return new Date(iso).toLocaleDateString();
@@ -192,7 +193,7 @@
       {#if confirmingLogoutOthers}
         <div class="flex flex-wrap items-center gap-2">
           <span class="text-sm text-text-secondary">
-            Sign out {others === 1 ? '1 other device' : `${others} other devices`}? You'll stay
+            Sign out {plural(others, 'other device', 'other devices')}? You'll stay
             signed in here.
           </span>
           <button