web: reset links to the default mode, and keep CN agents dial-only by default [CI]

POST /api/admin/links/reset clears every manual link setting and turns automatic linking on. In the default rules a listening node in CN ranks below a listening node elsewhere, so the CN side dials; the links are pushed again when a node's country is first resolved or changes.

backend/openapi/v1.json

@@ -4491,6 +4491,48 @@
         "x-moshiro-capability": "fleet.read"
       }
     },
+    "/api/admin/links/reset": {
+      "post": {
+        "tags": [
+          "admin-links"
+        ],
+        "summary": "Drop every manual link setting and turn automatic linking on: who dials whom follows the default rules again",
+        "operationId": "links_reset",
+        "responses": {
+          "200": {
+            "description": "OK",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/LinkMatrixDto"
+                }
+              }
+            }
+          },
+          "401": {
+            "description": "Unauthorized",
+            "content": {
+              "application/problem+json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ProblemDto"
+                }
+              }
+            }
+          },
+          "403": {
+            "description": "Forbidden",
+            "content": {
+              "application/problem+json": {
+                "schema": {
+                  "$ref": "#/components/schemas/ProblemDto"
+                }
+              }
+            }
+          }
+        },
+        "x-moshiro-capability": "fleet.write"
+      }
+    },
     "/api/admin/links/{dialer_id}/{listener_id}": {
       "put": {
         "tags": [