feat(stamdata): admin stamdata maintenance editor (beheer)

Realizes ADR-0004's "future low-code editor that commits a PR": an
admin-only stamdata maintenance editor built on the stamdata-as-code
foundation.

Backend: `professions` moves from a hardcoded C# dictionary to an embedded
`professions.json` data-file (typed as `ProfessionMapping`) with valid-time
(geldigVan/geldigTot, half-open). A generic, reflection-driven
StamdataCatalog/StamdataTable/StamdataFile describes every table so one
endpoint pair + one grid editor serve all of them; add a table in one line.
Two read-only, admin-gated endpoints (GET /stamdata, GET /stamdata/{table}
?peildatum=) — no runtime write path. Generic build gate
`Every_catalog_table_is_valid` (keys non-blank, no overlapping validity,
well-formed windows).

Frontend: new `beheer` context (route beheer/stamdata, capabilityGuard
'stamdata:edit'). A schema-driven grid editor edits rows locally; download()
emits {table}.json for the admin to commit as a reviewed PR (no mutation
command — the CI build + StamdataValidationTests stay the authority).

Full gate GREEN both sides; gen:api leaves no drift; new stamdata story
passes axe. See WP-29 + ADR-0004.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/tests/BigRegister.Tests/OrgTemplateEndpointTests.cs

@@ -201,7 +201,7 @@ public class OrgTemplateEndpointTests(TestWebApplicationFactory factory) : IClas
   {
     var res = await _client.SendAsync(Req(HttpMethod.Get, "/api/v1/me", role: "admin"));
     var me = await res.Content.ReadFromJsonAsync<MeDto>();
-    Assert.Equal(new[] { "orgtemplate:edit" }, me!.Capabilities);
+    Assert.Equal(new[] { "orgtemplate:edit", "stamdata:edit" }, me!.Capabilities);
   }
 
   [Fact]

backend/tests/BigRegister.Tests/StamdataEndpointTests.cs

@@ -0,0 +1,68 @@
+using System.Net;
+using System.Net.Http.Json;
+using BigRegister.Api.Contracts;
+using Microsoft.AspNetCore.Mvc.Testing;
+
+namespace BigRegister.Tests;
+
+/// <summary>
+/// The stamdata maintenance reads (ADR-0004): admin-only, generic (schema + rows), and the
+/// valid-time peildatum filter. The editor consumes these; the edit itself lands as a PR.
+/// </summary>
+public class StamdataEndpointTests(TestWebApplicationFactory factory) : IClassFixture<TestWebApplicationFactory>
+{
+  private readonly HttpClient _client = factory.CreateClient();
+
+  private HttpRequestMessage Req(HttpMethod method, string path, string? role = null)
+  {
+    var req = new HttpRequestMessage(method, path);
+    if (role is not null) req.Headers.Add("X-Role", role);
+    return req;
+  }
+
+  [Fact]
+  public async Task Stamdata_reads_are_admin_only()
+  {
+    Assert.Equal(HttpStatusCode.Forbidden, (await _client.SendAsync(Req(HttpMethod.Get, "/api/v1/stamdata"))).StatusCode);
+    Assert.Equal(HttpStatusCode.Forbidden, (await _client.SendAsync(Req(HttpMethod.Get, "/api/v1/stamdata/professions", role: "drafter"))).StatusCode);
+  }
+
+  [Fact]
+  public async Task Table_list_exposes_the_reflected_schema()
+  {
+    var res = await _client.SendAsync(Req(HttpMethod.Get, "/api/v1/stamdata", role: "admin"));
+    res.EnsureSuccessStatusCode();
+    var tables = (await res.Content.ReadFromJsonAsync<List<StamdataTableSummaryDto>>())!;
+    var professions = tables.Single(t => t.Id == "professions");
+    Assert.True(professions.Temporal);
+    Assert.True(professions.Columns[0].IsKey);
+    Assert.Equal("program", professions.Columns[0].Name);
+    Assert.Contains(professions.Columns, c => c.Name == "geldigVan" && c.Type == "date");
+  }
+
+  [Fact]
+  public async Task Table_returns_all_rows_without_a_peildatum()
+  {
+    var res = await _client.SendAsync(Req(HttpMethod.Get, "/api/v1/stamdata/professions", role: "admin"));
+    res.EnsureSuccessStatusCode();
+    var table = (await res.Content.ReadFromJsonAsync<StamdataTableDto>())!;
+    Assert.Equal(5, table.Rows.Count);
+  }
+
+  [Fact]
+  public async Task Peildatum_before_the_seed_windows_hides_every_row()
+  {
+    // Seed mappings start 2000-01-01; a 1999 peildatum yields none (valid-time filter works).
+    var res = await _client.SendAsync(Req(HttpMethod.Get, "/api/v1/stamdata/professions?peildatum=1999-01-01", role: "admin"));
+    res.EnsureSuccessStatusCode();
+    var table = (await res.Content.ReadFromJsonAsync<StamdataTableDto>())!;
+    Assert.Empty(table.Rows);
+  }
+
+  [Fact]
+  public async Task Unknown_table_is_404()
+  {
+    var res = await _client.SendAsync(Req(HttpMethod.Get, "/api/v1/stamdata/nope", role: "admin"));
+    Assert.Equal(HttpStatusCode.NotFound, res.StatusCode);
+  }
+}

backend/tests/BigRegister.Tests/StamdataValidationTests.cs

@@ -55,4 +55,16 @@ public class StamdataValidationTests
     var ids = PolicyQuestions.ManualSet.Select(q => q.Id).ToList();
     Assert.Equal(ids.Count, ids.Distinct().Count());
   }
+
+  // The GENERIC gate (ADR-0004): every table registered in the catalog is validated the
+  // same way — its JSON deserializes into its typed record, keys are non-blank and don't
+  // overlap in time, and valid-time windows are well-formed. A new stamdata type is covered
+  // the moment it's added to StamdataCatalog; no new test needed. A bad edit fails the build.
+  [Fact]
+  public void Every_catalog_table_is_valid()
+  {
+    foreach (var table in StamdataCatalog.All)
+      Assert.True(table.Validate().Count == 0,
+          $"Stamdata table '{table.Id}' has problems: {string.Join("; ", table.Validate())}");
+  }
 }