feat: Enhance SharePoint connection with error handling and verification

SharePointFunctions.ps1

@@ -39,10 +39,20 @@ function Connect-SharePoint {
             throw "Please enter a Site URL"
         }
 
-        # Simplified interactive auth
-        Connect-PnPOnline -Url $siteUrl -Interactive `
+        # Disconnect any existing connection first
+        Disconnect-PnPOnline -ErrorAction SilentlyContinue
+        
+        # Use modern authentication with device code flow
+        Connect-PnPOnline -Url $siteUrl -Interactive -ForceAuthentication `
+            -ErrorAction Stop `
             -WarningAction SilentlyContinue
         
+        # Verify connection
+        $web = Get-PnPWeb -ErrorAction Stop
+        if (-not $web) {
+            throw "Failed to connect to SharePoint site"
+        }
+        
         return $true
     }
     catch {