S-15c · Enforce MFA on the medewerker (Keycloak) realm (#158)

Closes #132.

Staff logins (behandel + beheer portals) now need a second factor; the citizen realms are unchanged.

**How:** every seeded medewerker carries a TOTP credential, which activates Keycloak's stock *conditional OTP* step in both the browser flow and the direct grant — no custom browser-flow JSON in the export. `CONFIGURE_TOTP` is a default required action so a medewerker added later must enrol first. ADR-0031 records the choice and, explicitly, that the shared fixture secret is a demo posture only.

**Tests (red first, 30c5279):**
- `check_realms.py` asserts the medewerker password-only grant is **refused**, then that password + TOTP succeeds and still carries the `behandelaar` role. It failed with `[MFA NOT ENFORCED]` against the old export.
- The three medewerker e2e logins move to `loginMedewerker()` (`tests/e2e/medewerker-login.ts`), which submits Keycloak's OTP prompt. Both TOTP implementations (Python `hmac`, Node `crypto`) are ~6 lines of RFC 6238 — no new dependency.

Verified locally against Keycloak 26.1: password-only → `invalid_grant`, password + code → 200, and the browser flow's `#otp` prompt accepts a computed code and issues an auth code.

## Definition of Done
- [x] Failing test/verify committed first; implementation makes it pass.
- [x] Conventional Commits referencing the issue (`refs #132`).
- [ ] CI green (verify-stack compose smoke + relevant checks).
- [x] `docker compose up` reaches green health within 3 minutes (Keycloak change is import-time only).
- [x] Docs touched (runbook, synthetic-data, demo-script) + ADR-0031 + demo note.
- [x] Closed by the merging PR (`closes #132`).

🤖 Generated with [Claude Code](https://claude.com/claude-code)Reviewed-on: #158

infra/keycloak/realms/medewerker-realm.json

@@ -2,6 +2,16 @@
   "realm": "medewerker",
   "enabled": true,
   "displayName": "Medewerkers",
+  "requiredActions": [
+    {
+      "alias": "CONFIGURE_TOTP",
+      "name": "Configure OTP",
+      "providerId": "CONFIGURE_TOTP",
+      "enabled": true,
+      "defaultAction": true,
+      "priority": 10
+    }
+  ],
   "roles": {
     "realm": [
       { "name": "behandelaar", "description": "Behandelt registratieaanvragen" },
@@ -43,7 +53,15 @@
       "lastName": "Behandelaar",
       "email": "merel@big.example.nl",
       "emailVerified": true,
-      "credentials": [{ "type": "password", "value": "test123", "temporary": false }],
+      "credentials": [
+        { "type": "password", "value": "test123", "temporary": false },
+        {
+          "type": "otp",
+          "userLabel": "seeded TOTP (fixture)",
+          "secretData": "{\"value\":\"BIGMEDEWERKEROTPSEED\"}",
+          "credentialData": "{\"subType\":\"totp\",\"digits\":6,\"counter\":0,\"period\":30,\"algorithm\":\"HmacSHA1\"}"
+        }
+      ],
       "realmRoles": ["behandelaar"]
     },
     {
@@ -53,7 +71,15 @@
       "lastName": "Teamlead",
       "email": "tom@big.example.nl",
       "emailVerified": true,
-      "credentials": [{ "type": "password", "value": "test123", "temporary": false }],
+      "credentials": [
+        { "type": "password", "value": "test123", "temporary": false },
+        {
+          "type": "otp",
+          "userLabel": "seeded TOTP (fixture)",
+          "secretData": "{\"value\":\"BIGMEDEWERKEROTPSEED\"}",
+          "credentialData": "{\"subType\":\"totp\",\"digits\":6,\"counter\":0,\"period\":30,\"algorithm\":\"HmacSHA1\"}"
+        }
+      ],
       "realmRoles": ["behandelaar", "teamlead"]
     },
     {
@@ -63,7 +89,15 @@
       "lastName": "Beheerder",
       "email": "bram@big.example.nl",
       "emailVerified": true,
-      "credentials": [{ "type": "password", "value": "test123", "temporary": false }],
+      "credentials": [
+        { "type": "password", "value": "test123", "temporary": false },
+        {
+          "type": "otp",
+          "userLabel": "seeded TOTP (fixture)",
+          "secretData": "{\"value\":\"BIGMEDEWERKEROTPSEED\"}",
+          "credentialData": "{\"subType\":\"totp\",\"digits\":6,\"counter\":0,\"period\":30,\"algorithm\":\"HmacSHA1\"}"
+        }
+      ],
       "realmRoles": ["beheerder"]
     }
   ]