chore(release): bump to 1.2.15

Version bump across Cargo/tauri/npm/snap/flake, metainfo release entry,
and TAG_DETAILS for 1.2.15. flake.nix hashes cleared (filled post-tag
via nix build once v1.2.15 exists).

cc

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "qbz-nix",
-  "version": "1.2.14",
+  "version": "1.2.15",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "qbz-nix",
-      "version": "1.2.14",
+      "version": "1.2.15",
       "hasInstallScript": true,
       "license": "MIT",
       "dependencies": {