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>

src/app/beheer/domain/stamdata.spec.ts

@@ -0,0 +1,86 @@
+import { describe, it, expect } from 'vitest';
+import { StamTable, activeOn, changeCounts, isValid, rowErrors, toJson } from './stamdata';
+
+const professions: StamTable = {
+  id: 'professions',
+  label: 'Opleiding → beroep',
+  temporal: true,
+  columns: [
+    { name: 'program', type: 'text', isKey: true, options: [] },
+    { name: 'beroep', type: 'text', isKey: false, options: [] },
+    { name: 'geldigVan', type: 'date', isKey: false, options: [] },
+    { name: 'geldigTot', type: 'date', isKey: false, options: [] },
+  ],
+};
+
+const row = (program: string, beroep: string, van: string, tot = ''): Record<string, string> => ({
+  program,
+  beroep,
+  geldigVan: van,
+  geldigTot: tot,
+});
+
+describe('activeOn (valid-time, half-open [van, tot))', () => {
+  it('includes a row whose window covers the date', () => {
+    expect(activeOn(professions, row('a', 'A', '2000-01-01'), '2020-01-01')).toBe(true);
+  });
+  it('excludes a row before its geldigVan', () => {
+    expect(activeOn(professions, row('a', 'A', '2000-01-01'), '1999-01-01')).toBe(false);
+  });
+  it('excludes on the geldigTot boundary (half-open)', () => {
+    expect(activeOn(professions, row('a', 'A', '2000-01-01', '2020-01-01'), '2020-01-01')).toBe(false);
+    expect(activeOn(professions, row('a', 'A', '2000-01-01', '2020-01-01'), '2019-12-31')).toBe(true);
+  });
+});
+
+describe('rowErrors / isValid (format only)', () => {
+  it('flags a blank key', () => {
+    expect(rowErrors(professions, [row('', 'A', '2000-01-01')])[0]).not.toBe('');
+  });
+  it('flags a missing geldigVan on a temporal table', () => {
+    expect(rowErrors(professions, [row('a', 'A', '')])[0]).not.toBe('');
+  });
+  it('flags geldigTot on or before geldigVan', () => {
+    expect(rowErrors(professions, [row('a', 'A', '2020-01-01', '2020-01-01')])[0]).not.toBe('');
+  });
+  it('passes a well-formed row', () => {
+    expect(isValid(professions, [row('a', 'A', '2000-01-01')])).toBe(true);
+  });
+});
+
+describe('changeCounts (diff against the loaded snapshot, by key)', () => {
+  const original = [row('a', 'A', '2000-01-01'), row('b', 'B', '2000-01-01')];
+  it('counts an added key', () => {
+    const draft = [...original, row('c', 'C', '2000-01-01')];
+    expect(changeCounts(professions, original, draft)).toEqual({ added: 1, removed: 0, edited: 0 });
+  });
+  it('counts a removed key', () => {
+    expect(changeCounts(professions, original, [original[0]])).toEqual({ added: 0, removed: 1, edited: 0 });
+  });
+  it('counts an edited cell', () => {
+    const draft = [row('a', 'CHANGED', '2000-01-01'), original[1]];
+    expect(changeCounts(professions, original, draft)).toEqual({ added: 0, removed: 0, edited: 1 });
+  });
+});
+
+describe('toJson (draft → file shape)', () => {
+  it('reconstructs an open-ended geldigTot as null and pretty-prints', () => {
+    const json = toJson(professions, [row('a', 'Arts', '2000-01-01')]);
+    expect(JSON.parse(json)).toEqual([
+      { program: 'a', beroep: 'Arts', geldigVan: '2000-01-01', geldigTot: null },
+    ]);
+    expect(json.endsWith('\n')).toBe(true);
+  });
+  it('coerces a number column', () => {
+    const table: StamTable = {
+      id: 't',
+      label: 't',
+      temporal: false,
+      columns: [
+        { name: 'code', type: 'text', isKey: true, options: [] },
+        { name: 'jaar', type: 'number', isKey: false, options: [] },
+      ],
+    };
+    expect(JSON.parse(toJson(table, [{ code: 'x', jaar: '2020' }]))).toEqual([{ code: 'x', jaar: 2020 }]);
+  });
+});