feat(api): expose PlayoutItem row id on the playout-items list DTO (#210)

The SPA needs the item's row id to call
GET /api/playouts/items/{id}/scheduling-context. Plumbed through
PlayoutItemViewModel -> PlayoutItemResponseModel as a nullable Id
(null for synthesized UNSCHEDULED gap rows, which are PlayoutGaps,
not PlayoutItems). Additive for existing consumers (Playouts.razor
reads the VM by property). Regenerated v1.json + v1.d.ts.

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

ErsatzTV/wwwroot/openapi/v1.json

@@ -19334,6 +19334,7 @@
       },
       "PlayoutItemResponseModel": {
         "required": [
+          "id",
           "title",
           "start",
           "finish",
@@ -19343,11 +19344,15 @@
         ],
         "type": "object",
         "properties": {
-          "title": {
+          "id": {
             "type": [
               "null",
-              "string"
-            ]
+              "integer"
+            ],
+            "format": "int32"
+          },
+          "title": {
+            "type": "string"
           },
           "start": {
             "type": "string",
@@ -19358,10 +19363,7 @@
             "format": "date-time"
           },
           "duration": {
-            "type": [
-              "null",
-              "string"
-            ]
+            "type": "string"
           },
           "fillerKind": {
             "oneOf": [