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.AppHost.Tests/golden/README.md

@@ -0,0 +1,14 @@
+# Golden saves
+
+`current/` is a school file of today's format. `legacy-no-native/` is the same school without
+`nativeLanguage`, so a missing field still has to mean "first language of the name set" rather
+than a new roll.
+
+These files live forever: a new save field must load `current/` and must not reshuffle
+`legacy-no-native/`. A real format change adds a new folder; it does not rewrite the old one.
+
+Regenerate after an intentional roster change (same commit):
+
+```
+WRITE_GOLDEN=1 dotnet test tests/HSchool.People.Tests/HSchool.People.Tests.csproj --filter Dump_HostSaveFixtures
+```