Enhance staffing management with uncovered teacher tracking

- Updated `protocol.md` to clarify the concept of uncovered subjects and the number of additional teachers required.
- Introduced `teachersShort` property in the `StaffingSubject` interface to indicate how many more teachers are needed for a subject.
- Enhanced localization strings to reflect the new uncovered teacher information in both English and Russian.
- Updated the management panel UI to display the number of teachers short for each uncovered subject.
- Revised the `Uncovered` method in the staffing logic to return detailed information about uncovered subjects, including the shortfall of teachers.
- Added tests to validate the new uncovered teacher tracking functionality and ensure accurate reporting in the staffing API.
- Marked related tasks as complete in the documentation for the golden fixtures phase.

src/HSchool.Server/Program.cs

@@ -70,6 +70,9 @@ if (app.Configuration.GetValue("HSchool:AllowSaveReload", false))
         return Results.NoContent();
     })
     .WithName("ReloadSchoolsFromDisk");
+
+    app.MapGet("/api/dev/saves-directory", (SchoolStore store) => Results.Json(new { path = store.DirectoryPath }))
+        .WithName("GetSavesDirectory");
 }
 
 // The realtime channel: one binary frame per protocol message, see docs/protocol.md.