fix(data): track EF migration Designer files (were gitignored)

The `*.designer.cs` ignore rule silently excluded EF Core migration
*.Designer.cs files, so only 1 of 11 was committed. Without the Designer
(which carries the [Migration] attribute), EF does not register a migration,
so a fresh clone / CI release build could not apply migrations — e.g.
GetAppSettings failed with "no such column: repo_import_folders", which the
Settings modal surfaced as "Worker offline".

Adds a .gitignore negation for **/Migrations/*.Designer.cs and commits the
10 missing Designer files (incl. the newly authored AddRepoImportFolders).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

.gitignore

@@ -45,6 +45,8 @@ artifacts/
 
 # Avalonia / XAML designer
 *.designer.cs
+# ...but EF Core migration Designer files are real source and must be tracked
+!**/Migrations/*.Designer.cs
 
 # Project-specific
 *.db