a11y: Tasks 2-6 -- App shell, Titlebar, ToggleSwitch, Stepper, animate.ts

- Add skip-to-content link and dynamic document title (App.svelte)
- Wrap titlebar in header landmark, enlarge traffic lights to 44px (Titlebar.svelte)
- Enlarge toggle switch to 52x28, improve OFF knob contrast (ToggleSwitch.svelte)
- Enlarge stepper buttons to 36px, add keyboard hold-to-repeat (Stepper.svelte)
- Add keyboard feedback to pressable, focus glow to glowHover (animate.ts)

src/lib/components/ToggleSwitch.svelte

@@ -20,14 +20,14 @@
   role="switch"
   aria-label={label}
   aria-checked={checked}
-  class="relative inline-flex h-[24px] w-[48px] shrink-0 cursor-pointer rounded-full
+  class="relative inline-flex h-[28px] w-[52px] min-h-[44px] shrink-0 cursor-pointer rounded-full
          transition-colors duration-200 ease-in-out"
   style="background: {checked ? $config.accent_color : '#1a1a1a'};"
   onclick={toggle}
 >
   <span
-    class="pointer-events-none inline-block h-[19px] w-[19px] rounded-full
+    class="pointer-events-none inline-block h-[22px] w-[22px] rounded-full
            shadow-sm transition-transform duration-200 ease-in-out
-           {checked ? 'translate-x-[26px] bg-white' : 'translate-x-[3px] bg-[#444]'} mt-[2.5px]"
+           {checked ? 'translate-x-[27px] bg-white' : 'translate-x-[3px] bg-[#666]'} mt-[3px]"
   ></span>
 </button>