chore: Semantic Versioning and a changelog from now on

Tags become three-part (v0.6.0), the header shows the full version and
pre-release tags no longer move :stable. CHANGELOG.md (Keep a Changelog)
starts with an Unreleased section; older versions will be added from the
history. The quantity field opens the number keypad on phones.

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

frontend/src/features/lists/SharedListsView.tsx

@@ -1123,6 +1123,7 @@ export const SharedListsView: React.FC<SharedListsViewProps> = ({ onRefreshGloba
             <div className="flex items-center gap-1.5 w-full sm:w-auto justify-end px-1 sm:px-0">
               <input
                 type="text"
+                inputMode="decimal"
                 value={newItemQty}
                 onChange={(e) => setNewItemQty(e.target.value.replace(/[^0-9.,xX]/g, ''))}
                 placeholder="Menge (z.B. 2)"