Add chat settings modal & reply previews

Introduce a full ChatSettingsModal component for managing group chats (rename/icon upload, add/remove members, toggle moderators, leave/delete) and wire it into ChatRoomPage with a settings button. Add reply preview support end-to-end: new ReplyToSerializer and members_detail in backend serializers, updated frontend Message model (reply_to now contains preview object), and UI changes to Message to render reply excerpts. Improve socket handling to attach reply previews when available. Tweak backend Dockerfile to optionally install Windows/corporate CA bundle only if present and move pip install after copying source. Add Czech translations and small tooling/.claude config enhancements.

.claude/settings.local.json

@@ -8,7 +8,8 @@
       "Bash(npx tsc *)",
       "Bash(npx eslint *)",
       "Bash(python -c ' *)",
-      "PowerShell(Get-ChildItem -Path \"c:\\\\Users\\\\bruno\\\\Documents\\\\GitHub\\\\vontor-cz\\\\frontend\\\\src\\\\components\\\\social\" -File -Recurse | Select-Object FullName, @{n='Lines';e={\\(Get-Content $_.FullName | Measure-Object -Line\\).Lines}} | Format-Table -AutoSize)"
+      "PowerShell(Get-ChildItem -Path \"c:\\\\Users\\\\bruno\\\\Documents\\\\GitHub\\\\vontor-cz\\\\frontend\\\\src\\\\components\\\\social\" -File -Recurse | Select-Object FullName, @{n='Lines';e={\\(Get-Content $_.FullName | Measure-Object -Line\\).Lines}} | Format-Table -AutoSize)",
+      "Bash(grep -E \"\\\\.\\(ts|tsx\\)$\")"
     ]
   }
 }