Content/authoring: concealment colliders, scene + material tweaks, ignore third-party asset packs

- Generated concealment colliders for The Room (Fortuny ON base/top)
- Main + The Room scene edits, Wall_White material variants
- ProjectSettings churn (PackageManager, ProBuilder settings)
- .gitignore: exclude imported Allsky / ArchVizPRO Vol.6 / Isle of Assets packs

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

ProjectSettings/PackageManagerSettings.asset

@@ -12,11 +12,13 @@ MonoBehaviour:
   m_Script: {fileID: 13964, guid: 0000000000000000e000000000000000, type: 0}
   m_Name: 
   m_EditorClassIdentifier: 
-  m_EnablePreviewPackages: 0
-  m_EnablePackageDependencies: 0
+  m_EnablePreReleasePackages: 0
   m_AdvancedSettingsExpanded: 1
   m_ScopedRegistriesSettingsExpanded: 1
+  m_SeeAllPackageVersions: 0
+  m_DismissPreviewPackagesInUse: 0
   oneTimeWarningShown: 0
+  oneTimePackageErrorsPopUpShown: 0
   m_Registries:
   - m_Id: main
     m_Name: 
@@ -24,20 +26,15 @@ MonoBehaviour:
     m_Scopes: []
     m_IsDefault: 1
     m_Capabilities: 7
+    m_ConfigSource: 0
+    m_Compliance:
+      m_Status: 0
+      m_Violations: []
   m_UserSelectedRegistryName: 
   m_UserAddingNewScopedRegistry: 0
   m_RegistryInfoDraft:
-    m_ErrorMessage: 
-    m_Original:
-      m_Id: 
-      m_Name: 
-      m_Url: 
-      m_Scopes: []
-      m_IsDefault: 0
-      m_Capabilities: 0
     m_Modified: 0
-    m_Name: 
-    m_Url: 
-    m_Scopes:
-    - 
-    m_SelectedScopeIndex: 0
+    m_ErrorMessage: 
+    m_UserModificationsInstanceId: -896
+    m_OriginalInstanceId: -898
+  m_LoadAssets: -1