feat(events): open the event contract to modules (Phase 7)

MODULE_API 1.10.0. Four names forwarded on the module-facing `api` --
registerEventActions, registerEventBudgets, registerEventLeases and
registerEventOptionSources -- one new route, and one rule made real: a
`cost()` naming a dimension no module declared is refused.

Only one of the four is new machinery. The action registry has staged
core's three actions on every boot since Phase 1; what it never had was a
way in, because loader.js builds its own `api` facade and had no method
that delegated to it. So the registry a module now reaches is one that has
been exercised on every boot for six phases.

Four decisions, settled 2026-09-03, all as recommended:

- Option sources are their own registration, modelled on registerAudiences,
  because a catalog has more than one consumer.
- An undeclared dimension is refused -- at save, at the dry run and at
  dispatch -- with its own code, because the fix is a module's declaration
  and not a deployment's cap.
- A lease is declared here and acquired by nothing; the ledger is Phase 8.
- Core registers core.options.legs, so an announce leg is a dropdown rather
  than the free-text box whose typo Phase 6's walk caught mid-run.

Proved with a throwaway module through the real loader, not with module-uo:
eventModuleContract.test.js writes a module to a real directory and lets the
loader scan it, covering all five envelope failure shapes, verify: true, the
four id spaces and dormancy on uninstall.

The live walk found the one defect nothing else could: the option-source
loader wrote its "already asked?" guard inside a setState updater and read
it on the next line, so the request was never made and the field sat on
"Reading the list..." for ever. It is a useRef now.

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01T6t8mrAWhZU5vnyYgZTMtL

server/swagger/swagger-output.json

@@ -3958,6 +3958,89 @@
         ]
       }
     },
+    "/api/v1/admin/events/catalog/options/{sourceId}": {
+      "get": {
+        "tags": [
+          "Admin · Events"
+        ],
+        "summary": "Resolve the values behind a param option source",
+        "description": "EVENTS.md F, Param option sources (Phase 7). A param may declare a `source`, and this is what answers it: the module that registered the source resolves the list, so an authoring field is a dropdown of real landmarks or creatures rather than a text box an operator can typo. A refusal comes back as a 200 with `ok: false` and a `reason` -- deliberately, because a source that cannot answer degrades its field to free text with a visible warning rather than blocking the form, and an authoring screen a sidecar outage can make unusable is a worse failure than the typo the dropdown prevents. Values are resolved per request rather than cached in the catalog, because a source can be slow or down and must not take the whole catalog with it.",
+        "parameters": [
+          {
+            "name": "sourceId",
+            "in": "path",
+            "required": true,
+            "schema": {
+              "type": "string"
+            }
+          }
+        ],
+        "responses": {
+          "200": {
+            "description": "The options, or the reason there are none",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "type": "object",
+                  "properties": {
+                    "ok": {
+                      "type": "boolean"
+                    },
+                    "id": {
+                      "type": "string"
+                    },
+                    "label": {
+                      "type": "string"
+                    },
+                    "owner": {
+                      "type": "string"
+                    },
+                    "reason": {
+                      "type": "string"
+                    },
+                    "options": {
+                      "type": "array",
+                      "items": {
+                        "type": "object",
+                        "properties": {
+                          "value": {
+                            "type": "string"
+                          },
+                          "label": {
+                            "type": "string"
+                          },
+                          "group": {
+                            "type": "string"
+                          }
+                        }
+                      }
+                    }
+                  }
+                }
+              }
+            }
+          },
+          "403": {
+            "description": "Not staff",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/Error"
+                }
+              }
+            }
+          }
+        },
+        "security": [
+          {
+            "cookieAuth": []
+          },
+          {
+            "bearerAuth": []
+          }
+        ]
+      }
+    },
     "/api/v1/admin/events/runs": {
       "get": {
         "tags": [