chore(release): bump version to 1.2.10 + tag notes

Hotfix on top of 1.2.9 to address the gapless-play regression
introduced by dee987c1a's tightened isGaplessTransition gate combined
with a long-standing race in the player's transition-swap atomics.

Bumped:
- src-tauri/Cargo.toml + Cargo.lock
- src-tauri/tauri.conf.json
- package.json + package-lock.json
- snapcraft.yaml (version + source-tag) — packaging/snap/snapcraft.yaml
  follows automatically via symlink
- packaging/flatpak/com.blitzfc.qbz.metainfo.xml (new release entry)

cc

packaging/flatpak/com.blitzfc.qbz.metainfo.xml

@@ -69,6 +69,11 @@
     </screenshot>
   </screenshots>
   <releases>
+    <release version="1.2.10" date="2026-04-29">
+      <description>
+        <p>Fix an issue with gapless play introduced by a new feature in 1.2.9.</p>
+      </description>
+    </release>
     <release version="1.2.9" date="2026-04-29">
       <description>
         <p>Quiet Polish: QConnect cleanup, Linux tray for everyone, sticky and sidebar fixes.</p>