Celebrate a logged pee/poo with emoji confetti

Tapping the pee or poo quick-log button now sets off a short burst of 💧/💩
particles from the button — pure DOM + CSS, pointer-events:none so it never
blocks taps, particles self-remove on animation end. It honours
prefers-reduced-motion, and there's a "Pee/poo confetti" switch in Settings
(device-local, on by default) to turn it off.

src/index.html

@@ -335,6 +335,10 @@
           <span>Dark mode</span>
           <input type="checkbox" id="settings-theme" role="switch" class="switch" />
         </label>
+        <label class="toggle-row">
+          <span>Pee/poo confetti 💩</span>
+          <input type="checkbox" id="settings-confetti" role="switch" class="switch" />
+        </label>
         <menu>
           <button value="cancel" class="ghost">Cancel</button>
           <button value="save" id="settings-save">Save</button>