Release v0.9.1: Linux build fixes and branding update

- Bump version to 0.9.1 in all files
- Add detailed CHANGELOG for v0.9.1 with Linux AppImage build fixes
- Fix desktop notification: "Electrum" → "Pallectrum"

Fixes reproducible builds with ELECBUILD_COMMIT and improves
AppImage filename determinism.

electrum/plugins/timelock_recovery/manifest.json

@@ -4,5 +4,5 @@
   "author": "orenz0@protonmail.com",
   "available_for": ["qt"],
   "icon":"timelock_recovery_60.png",
-  "version": "0.9.0"
+  "version": "0.9.1"
 }