fix(sw): bump the cache version for the F13 bundle

The shell is served cache-first and CACHE_VERSION had sat at v1 through four
commits that changed main.js, so a returning reader kept the old bundle: none of
the new UI reached them and the page looked simply unchanged. sw.js says to bump
it on any shell change and I did not.

Also tells the reader why the game list holds only tracked games when they have
none of their own yet — the list is nine games we cover with no hint that a game
of theirs has to exist before an event can be filed under it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

src/client/components/CustomForms.tsx

@@ -215,6 +215,16 @@ export function EventForm({
         </select>
       </label>
 
+      {/* Otherwise the list is nine games we track and no sign of why none of
+          them is theirs — the reader who came here to add a game we don't cover
+          has no way of knowing they need to make it first. */}
+      {Object.keys(customGames).length === 0 && (
+        <p className="mt-1.5 text-xs leading-relaxed text-faint">
+          These are the games we track. To file this under a game of your own,
+          cancel and add the game first.
+        </p>
+      )}
+
       <label className={`${labelClass()} mt-3`}>
         What is it
         <input