feat(04-07): add Phase 4 localization, shared dialogs, and example CSV resources

- Add 80+ Phase 4 EN/FR localization keys to Strings.resx and Strings.fr.resx (tabs, transfer, bulkmembers, bulksites, folderstruct, templates, bulk-shared, folderbrowser)
- Add ResourceManager property accessors for all new keys to Strings.Designer.cs
- Create ConfirmBulkOperationDialog (XAML + code-behind) with Proceed/Cancel buttons
- Create FolderBrowserDialog (XAML + code-behind) with lazy-loading TreeView of SharePoint libraries/folders
- Bundle bulk_add_members.csv, bulk_create_sites.csv, folder_structure.csv as EmbeddedResource in csproj

SharepointToolbox/Resources/bulk_add_members.csv

@@ -0,0 +1,8 @@
+GroupName,GroupUrl,Email,Role
+Marketing Team,https://contoso.sharepoint.com/sites/Marketing,user1@contoso.com,Member
+Marketing Team,https://contoso.sharepoint.com/sites/Marketing,manager@contoso.com,Owner
+HR Team,https://contoso.sharepoint.com/sites/HR,hr-admin@contoso.com,Owner
+HR Team,https://contoso.sharepoint.com/sites/HR,recruiter@contoso.com,Member
+HR Team,https://contoso.sharepoint.com/sites/HR,analyst@contoso.com,Member
+IT Support,https://contoso.sharepoint.com/sites/IT,sysadmin@contoso.com,Owner
+IT Support,https://contoso.sharepoint.com/sites/IT,helpdesk@contoso.com,Member

SharepointToolbox/Resources/bulk_create_sites.csv

@@ -0,0 +1,6 @@
+Name;Alias;Type;Template;Owners;Members
+Projet Alpha;projet-alpha;Team;;admin@contoso.com;user1@contoso.com, user2@contoso.com
+Projet Beta;projet-beta;Team;;admin@contoso.com;user3@contoso.com, user4@contoso.com
+Communication RH;comm-rh;Communication;;rh-admin@contoso.com;manager1@contoso.com, manager2@contoso.com
+Equipe Marketing;equipe-marketing;Team;;marketing-lead@contoso.com;designer@contoso.com, redacteur@contoso.com
+Portail Intranet;portail-intranet;Communication;;it-admin@contoso.com;

SharepointToolbox/Resources/folder_structure.csv

@@ -0,0 +1,20 @@
+Level1;Level2;Level3;Level4
+Administration;;;
+Administration;Comptabilite;;
+Administration;Comptabilite;Factures;
+Administration;Comptabilite;Bilans;
+Administration;Ressources Humaines;;
+Administration;Ressources Humaines;Contrats;
+Administration;Ressources Humaines;Fiches de paie;
+Projets;;;
+Projets;Projet Alpha;;
+Projets;Projet Alpha;Documents;
+Projets;Projet Alpha;Livrables;
+Projets;Projet Beta;;
+Projets;Projet Beta;Documents;
+Communication;;;
+Communication;Interne;;
+Communication;Interne;Notes de service;
+Communication;Externe;;
+Communication;Externe;Communiques de presse;
+Communication;Externe;Newsletter;