fix: comprehensive UUID/username persistence bug fixes (#252)

* fix: comprehensive UUID/username persistence bug fixes

Major fixes for UUID/skin reset issues that caused players to lose cosmetics:

Core fixes:
- Username rename now preserves UUID (atomic rename, not new identity)
- Atomic config writes with backup/recovery system
- Case-insensitive UUID lookup with case-preserving storage
- Pre-launch validation blocks play if no username configured
- Removed saveUsername calls from launch/install flows

UUID Modal fixes:
- Fixed isCurrent badge showing on wrong user
- Added switch identity button to change between saved usernames
- Fixed custom UUID input using unsaved DOM username
- UUID list now refreshes when player name changes
- Enabled copy/paste in custom UUID input field

UI/UX improvements:
- Added translation keys for switch username functionality
- CSS user-select fix for UUID input fields
- Allowed Ctrl+V/C/X/A shortcuts in Electron

Files: config.js, gameLauncher.js, gameManager.js, playerManager.js,
launcher.js, settings.js, main.js, preload.js, style.css, en.json

See UUID_BUGS_FIX_PLAN.md for detailed bug list (18 bugs, 16 fixed)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* feat(i18n): add switch username translations to all locales

Added translation keys for username switching functionality:
- notifications.noUsername
- notifications.switchUsernameSuccess
- notifications.switchUsernameFailed
- notifications.playerNameTooLong
- confirm.switchUsernameTitle
- confirm.switchUsernameMessage
- confirm.switchUsernameButton

Languages updated: de-DE, es-ES, fr-FR, id-ID, pl-PL, pt-BR, ru-RU, sv-SE, tr-TR

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

* docs: move UUID_BUGS_FIX_PLAN.md to docs folder

* docs: update UUID_BUGS_FIX_PLAN with complete fix details

---------

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

GUI/locales/de-DE.json

@@ -211,7 +211,11 @@
     "modsDeleteFailed": "Mod konnte nicht gelöscht werden: {error}",
     "modsModNotFound": "Mod-Informationen nicht gefunden",
     "hwAccelSaved": "Hardware-Beschleunigungseinstellung gespeichert",
-    "hwAccelSaveFailed": "Hardware-Beschleunigungseinstellung konnte nicht gespeichert werden"
+    "hwAccelSaveFailed": "Hardware-Beschleunigungseinstellung konnte nicht gespeichert werden",
+    "noUsername": "Kein Benutzername konfiguriert. Bitte speichere zuerst deinen Benutzernamen.",
+    "switchUsernameSuccess": "Erfolgreich zu \"{username}\" gewechselt!",
+    "switchUsernameFailed": "Benutzername konnte nicht gewechselt werden",
+    "playerNameTooLong": "Spielername darf maximal 16 Zeichen haben"
   },
   "confirm": {
     "defaultTitle": "Aktion bestätigen",
@@ -226,7 +230,10 @@
     "deleteUuidButton": "Löschen",
     "uninstallGameTitle": "Spiel deinstallieren",
     "uninstallGameMessage": "Möchtest du Hytale wirklich deinstallieren? Alle Spieldateien werden gelöscht.",
-    "uninstallGameButton": "Deinstallieren"
+    "uninstallGameButton": "Deinstallieren",
+    "switchUsernameTitle": "Identität wechseln",
+    "switchUsernameMessage": "Zu Benutzername \"{username}\" wechseln? Dies ändert deine aktuelle Spieleridentität.",
+    "switchUsernameButton": "Wechseln"
   },
   "progress": {
     "initializing": "Initialisiere...",