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.

tests/HSchool.People.Tests/GoldenRosterTests.cs

@@ -0,0 +1,27 @@
+namespace HSchool.People.Tests;
+
+public class GoldenRosterTests
+{
+    private const string Native = "RussianLanguage";
+
+    [Fact]
+    public void GoldenRoster_MatchesFixture()
+    {
+        var roster = Fixtures.Generate(Fixtures.Classrooms(4));
+        var actual = RosterFingerprint.Format(roster, Fixtures.SchoolSeed, "Slavic", Native);
+        var relative = Path.Combine("golden", "roster.txt");
+        var output = Path.Combine(AppContext.BaseDirectory, relative);
+        var source = Path.Combine(Fixtures.RepoRoot(), "tests", "HSchool.People.Tests", relative);
+
+        if (string.Equals(Environment.GetEnvironmentVariable("WRITE_GOLDEN"), "1", StringComparison.Ordinal))
+        {
+            Directory.CreateDirectory(Path.GetDirectoryName(source)!);
+            File.WriteAllText(source, actual);
+            Directory.CreateDirectory(Path.GetDirectoryName(output)!);
+            File.WriteAllText(output, actual);
+        }
+
+        Assert.True(File.Exists(output), $"Golden roster is missing at {output}.");
+        RosterFingerprint.AssertEqual(File.ReadAllText(output), actual);
+    }
+}