chore(release): bump version to 1.2.7 + release notes

Bumped:
- src-tauri/Cargo.toml + Cargo.lock
- src-tauri/tauri.conf.json
- package.json + package-lock.json
- snapcraft.yaml
- flake.nix (qbzVersion, hashes cleared for nix users to regenerate)

Added:
- packaging/flatpak/com.blitzfc.qbz.metainfo.xml (1.2.7 entry)
- docs/release-1.2.7/TAG_DETAILS.md (release notes — 1.2.7 preamble
  on top of the full 1.2.6 + 1.2.5 content)

cc

package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "qbz-nix",
-  "version": "1.2.6",
+  "version": "1.2.7",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "qbz-nix",
-      "version": "1.2.6",
+      "version": "1.2.7",
       "license": "MIT",
       "dependencies": {
         "@icons-pack/svelte-simple-icons": "^7.2.0",