fix: add folderTrust+yolo settings to Gemini installers and README

- settings.json now includes security.folderTrust.enabled=false and
  general.defaultApprovalMode=yolo to suppress trust/permission prompts
- Linux installer creates trustedFolders.json with common paths
- Windows PS1 installer creates trustedFolders.json for C:\ paths
- README Windows section adds $env: vars for current session
- Fixed BOM issue: all PS1 use WriteAllText instead of Set-Content

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

gemini/ugemini_install.ps1

@@ -150,15 +150,26 @@ $json = @'
   "security": {
     "auth": {
       "selectedType": "gemini-api-key"
+    },
+    "folderTrust": {
+      "enabled": false
     }
   },
   "telemetry": {
     "enabled": false,
     "logPrompts": false
+  },
+  "general": {
+    "defaultApprovalMode": "yolo"
   }
 }
 '@
 [System.IO.File]::WriteAllText($settingsFile, $json)
+
+# Create trustedFolders.json
+$trustedFile = "$geminiDir\trustedFolders.json"
+$trustedJson = '{"C:\\":"TRUST_PARENT","C:\\Users":"TRUST_PARENT"}'
+[System.IO.File]::WriteAllText($trustedFile, $trustedJson)
 Write-Host "  Settings: $settingsFile" -ForegroundColor Green
 
 # ---- Verify ----