feat(focus-timer): integrate with float window + add pop-out button

Jake's feedback on Phase 1: make the timer pinnable / always-on-top,
combined with the existing Now-list pop-out. Two changes:

1. Mount <FocusTimer /> in src/routes/float/+layout@.svelte so the
   running countdown stays visible in the always-on-top float window
   alongside the WIP task list. No content change to the float page
   itself — the timer is a global overlay.

2. Add a pop-out icon to the main-window focus timer that opens the
   existing /float route via window.open. One click → timer + Now
   list pinned on top without touching main window focus. Hidden
   inside the float window itself (detected via URL) so you cannot
   recursively pop out.

Result matches the Todo float-out UX the user already knows:
click ExternalLink, you get a small always-on-top window with
tasks + a live countdown ring in the top-right.

src/routes/float/+layout@.svelte

@@ -12,6 +12,7 @@
     PREFERENCES_CHANGED_EVENT,
   } from "$lib/stores/preferences.svelte.js";
   import Titlebar from "$lib/components/Titlebar.svelte";
+  import FocusTimer from "$lib/components/FocusTimer.svelte";
   import { loadOsInfo, isLinux } from "$lib/utils/osInfo.js";
 
   let { children } = $props();
@@ -90,3 +91,9 @@
     {@render children()}
   </div>
 </div>
+
+<!-- Focus timer also visible in the always-on-top float window so a
+     running countdown stays with the Now list. The component is a
+     global overlay (position: fixed) so it pins to the top-right of
+     this window independent of the Tasks content below. -->
+<FocusTimer />