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.

docs/protocol.md

@@ -276,7 +276,9 @@ teaching it. So a second teacher of a subject halves what the first one carries
 
 A subject appears in `uncovered` when nobody teaches it **or** when the people who do cannot
 between them carry its hours (`maxWeeklyHours` each). Both mean the same thing to a player:
-those lessons will not happen.
+those lessons will not happen. `teachersShort` is how many more people that subject still
+needs — primary school on a vanilla map is three, and hiring the second teacher leaves it at
+one.
 
 ```json
 {
@@ -289,7 +291,8 @@ those lessons will not happen.
       "label": "Математика",
       "gradeMin": 5,
       "gradeMax": 11,
-      "hoursPerWeek": 5
+      "hoursPerWeek": 5,
+      "teachersShort": 1
     }
   ],
   "applicants": [