feat(behandelportal): WP-65a beoordeling detail (read) + fix unreachable medewerker login

New GET /beoordeling/{id} shows one aanvraag's status, linked documents, and a
canBesluiten decision flag, gated by the same CanBeoordelen capability as the
werkvoorraad list. Reads through IZaakSource.ListCases rather than a new seam
method (WP-66 needs one anyway for the real write); owner BSN is masked.

Fixes a real gap found while wiring this up: the behandelportal's login was still
WP-61's copied citizen/BSN DigiD flow, so nothing ever sent X-Medewerker and the
werkvoorraad screen (WP-64) always denied in a real browser. A dev-only
medewerkerInterceptor (mirrors the existing ?role= stand-in as ?rollen=) fixes that.

WP-65's own Risks note authorized splitting read from write across sessions given
its size; this is the read half. The decision-recording mutation is next (65b).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

backend/swagger.json

@@ -798,6 +798,48 @@
         }
       }
     },
+    "/api/v1/beoordeling/{id}": {
+      "get": {
+        "tags": [
+          "BigRegister.Api, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null"
+        ],
+        "parameters": [
+          {
+            "name": "id",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "OK",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/BeoordelingViewDto"
+                }
+              }
+            }
+          },
+          "403": {
+            "description": "Forbidden",
+            "content": {
+              "application/problem+json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ProblemDetails"
+                }
+              }
+            }
+          },
+          "404": {
+            "description": "Not Found"
+          }
+        }
+      }
+    },
     "/api/v1/admin/cases/{id}": {
       "delete": {
         "tags": [
@@ -1606,6 +1648,52 @@
         },
         "additionalProperties": false
       },
+      "BeoordelingDecisionsDto": {
+        "type": "object",
+        "properties": {
+          "canBesluiten": {
+            "type": "boolean"
+          }
+        },
+        "additionalProperties": false
+      },
+      "BeoordelingDocumentDto": {
+        "type": "object",
+        "properties": {
+          "documentId": {
+            "type": "string",
+            "nullable": true
+          },
+          "categoryId": {
+            "type": "string",
+            "nullable": true
+          },
+          "fileName": {
+            "type": "string",
+            "nullable": true
+          }
+        },
+        "additionalProperties": false
+      },
+      "BeoordelingViewDto": {
+        "type": "object",
+        "properties": {
+          "aanvraag": {
+            "$ref": "#/components/schemas/ApplicationSummaryDto"
+          },
+          "documenten": {
+            "type": "array",
+            "items": {
+              "$ref": "#/components/schemas/BeoordelingDocumentDto"
+            },
+            "nullable": true
+          },
+          "decisions": {
+            "$ref": "#/components/schemas/BeoordelingDecisionsDto"
+          }
+        },
+        "additionalProperties": false
+      },
       "BriefDecisionsDto": {
         "type": "object",
         "properties": {