Tighten TimeSpinner spacing and fix build warnings

Reduce gap between numbers and h/m unit labels in the workday
schedule spinners. Remove unused parse_hour function and fix
Svelte state_referenced_locally warning in BreakScreen.

src/lib/components/BreakScreen.svelte

@@ -13,7 +13,7 @@
 
   let { standalone = false }: Props = $props();
 
-  const appWindow = standalone ? getCurrentWebviewWindow() : null;
+  const appWindow = $derived(standalone ? getCurrentWebviewWindow() : null);
 
   let currentActivity = $state<BreakActivity>(pickRandomActivity());
   let activityCycleTimer: ReturnType<typeof setInterval> | null = null;