feat(events): publish runId on a public calendar run entry (Rust D125)

A run entry on GET /public/events now names its run, the same id the
event page already publishes on each occurrence and `?run=` takes. A
Rust map marker carries core's run id and nothing else about its event,
so without this the app could only find the event by fetching every
event page.

A projected entry has no runId: nothing is committed to it. Rehearsals
and unlisted events stay absent from the calendar, so their markers
stay unlinked. The web calendar ignores the field.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E14m6SuuY6i1vASFeGDBeY

server/swagger/swagger-output.json

@@ -26295,6 +26295,23 @@
                   }
                 }
               },
+              "runId": {
+                "type": "object",
+                "properties": {
+                  "type": {
+                    "type": "string",
+                    "example": "integer"
+                  },
+                  "example": {
+                    "type": "number",
+                    "example": 3692
+                  },
+                  "description": {
+                    "type": "string",
+                    "example": "Runs only: the run this entry is, the same id `PublicEventOccurrence.runId` carries and `/events/{slug}?run=` takes. A projected entry has none, because nothing is committed to it."
+                  }
+                }
+              },
               "title": {
                 "type": "object",
                 "properties": {