Enhance school creation and staffing management with native language support

- Updated protocol documentation to include `nativeLanguages` in `nameSets` and added `nativeLanguage` to school creation options.
- Enhanced the UI for school creation to allow selection of native languages, improving user experience.
- Revised API interfaces to accommodate new native language features, ensuring proper data handling.
- Improved localization strings to support new native language functionalities in both English and Russian.
- Updated tests to validate the new native language features and ensure robust functionality in staffing scenarios.

docs/protocol.md

@@ -77,8 +77,10 @@ single seats field on a homeroom and the old slot rows on everything else.
 Things carry `pupilSlots` — how many pupils that thing hosts. The snapshot's per-node pupil-slot
 total is computed on the server.
 
-`nameSets` is the list of placeable name packs (`defName` + label). The create dialog picks one;
-it is independent of the UI language.
+`nameSets` is the list of placeable name packs (`defName` + label + `nativeLanguages`). Each
+`nativeLanguages` entry is a skill (`defName` + label). The create dialog picks a name set and a
+native language; the language list comes from that set (vanilla Slavic: Russian, Belarusian,
+Ukrainian). It is independent of the UI language.
 
 `subjects` is the list of placeable subjects (`defName`, label, `gradeMin`/`gradeMax`,
 `hoursPerWeek`, `skills` with shares, and optional `room`). `room` is the RoomDef the lesson
@@ -104,7 +106,8 @@ Body:
   "startDate": "2012-03-31T06:00:00Z",
   "modIds": [],
   "map": null,
-  "nameSetId": "Slavic"
+  "nameSetId": "Slavic",
+  "nativeLanguage": null
 }
 ```
 
@@ -112,6 +115,8 @@ Body:
 pack set's default layout. A supplied map is validated as a connected yard-and-rooms graph.
 `nameSetId` is a `NameSetDef`; omit it to use the first placeable set in the catalog (vanilla:
 `Slavic`). Unknown ids return `400` `unknown-name-set`.
+`nativeLanguage` is a skill from that set's `nativeLanguages`. Omit it (or send `null`) to pick
+one from the school seed. An id that is not in the set returns `400` `unknown-native-language`.
 
 | Status | Meaning |
 | --- | --- |
@@ -122,6 +127,7 @@ pack set's default layout. A supplied map is validated as a connected yard-and-r
 | `400` `unknown-mod` | An extra pack id is missing under `mods/`. |
 | `400` `invalid-catalog` | The selected packs could not be loaded. |
 | `400` `unknown-name-set` | `nameSetId` is not a placeable `NameSetDef` in those packs. |
+| `400` `unknown-native-language` | `nativeLanguage` is not in that name set's `nativeLanguages`. |
 | `409` `school-limit-reached` | `maxSchools` schools already exist. |
 
 Failures are RFC 7807 problem details with an extra `code` field — that is what the UI switches on.
@@ -334,8 +340,9 @@ ids that are in neither place stay `404` `unknown-person`.
 ### `POST /api/schools/{id}/staff/hire`
 
 Body: `{ "personId": "a0.p0", "position": "Teacher" }`. Goes through the school's mailbox.
-On success returns the same payload as `GET .../staffing`. `Teacher` needs no room opening;
-other positions fill the first free `RoomDef.positions` slot of that kind.
+On success returns the same payload as `GET .../staffing`, so it takes the same `?lang=ru|en`.
+`Teacher` needs no room opening; other positions fill the first free `RoomDef.positions` slot
+of that kind.
 
 | Status | `code` | When |
 | --- | --- | --- |
@@ -351,7 +358,8 @@ other positions fill the first free `RoomDef.positions` slot of that kind.
 
 ### `POST /api/schools/{id}/staff/{personId}/subjects`
 
-Body: `{ "subject": "Mathematics" }`. Teachers only. Same success payload as GET staffing.
+Body: `{ "subject": "Mathematics" }`. Teachers only. Same success payload as GET staffing,
+and the same `?lang=ru|en`.
 
 | Status | `code` | When |
 | --- | --- | --- |
@@ -363,8 +371,8 @@ Body: `{ "subject": "Mathematics" }`. Teachers only. Same success payload as GET
 
 ### `DELETE /api/schools/{id}/staff/{personId}/subjects/{subject}`
 
-Removes one assignment. Payroll drops when the subject was not the only one. Unknown
-assignment is `404` `unknown-assignment`.
+Removes one assignment. Payroll drops when the subject was not the only one. Same success
+payload and `?lang=ru|en` as the other two. Unknown assignment is `404` `unknown-assignment`.
 
 ### `GET /api/schools/{id}/timetable`