feat(public): version/health surfacing for the app first-run probe

Expose a small backend identity/version descriptor (§8.4 of the Android plan)
so a client can positively recognize a Runic Gateway backend on first-run and
run a version-mismatch guard, instead of inferring from an incidental shape.

- New config/version.js: { service: 'runic-gateway', api: 'v1', server: <pkg> }.
- GET /public/status now includes a `version` block (the app already calls this
  on first-run, so it gets identity + version in one round trip).
- New GET /public/version: a lightweight, DB-free identity endpoint — the
  canonical target for the version guard and a cheap liveness check.
- Swagger: PublicVersion schema + version on PublicStatus; /version annotated.
- test/publicVersion.test.js covers the config shape and the DB-free 200.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NgyHnrNa8WwG3doxvxjuCr

server/swagger/swagger-output.json

@@ -1662,7 +1662,7 @@
           "Public"
         ],
         "summary": "Site mode / status",
-        "description": "Current site mode (live or maintenance) so the client can show the maintenance page.",
+        "description": "Current site mode (live or maintenance) so the client can show the maintenance page, plus a version block (service id + API/server versions) for a client first-run probe and version-mismatch guard.",
         "responses": {
           "200": {
             "description": "Site status",
@@ -1680,6 +1680,27 @@
         }
       }
     },
+    "/api/v1/public/version": {
+      "get": {
+        "tags": [
+          "Public"
+        ],
+        "summary": "Backend identity + version",
+        "description": "Lightweight, DB-free descriptor of this backend: a stable service id and the API/server versions. A client uses it to recognize a Runic Gateway backend on first-run and to run a version-mismatch guard. Doubles as a cheap liveness check.",
+        "responses": {
+          "200": {
+            "description": "Backend version",
+            "content": {
+              "application/json": {
+                "schema": {
+                  "$ref": "#/components/schemas/PublicVersion"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
     "/api/v1/public/contact": {
       "post": {
         "tags": [
@@ -13907,6 +13928,78 @@
                     "example": ""
                   }
                 }
+              },
+              "version": {
+                "$ref": "#/components/schemas/PublicVersion"
+              }
+            }
+          }
+        }
+      },
+      "PublicVersion": {
+        "type": "object",
+        "properties": {
+          "type": {
+            "type": "string",
+            "example": "object"
+          },
+          "description": {
+            "type": "string",
+            "example": "Backend identity + version (GET /public/version; also embedded in /public/status)."
+          },
+          "properties": {
+            "type": "object",
+            "properties": {
+              "service": {
+                "type": "object",
+                "properties": {
+                  "type": {
+                    "type": "string",
+                    "example": "string"
+                  },
+                  "example": {
+                    "type": "string",
+                    "example": "runic-gateway"
+                  },
+                  "description": {
+                    "type": "string",
+                    "example": "Stable backend identifier for first-run recognition."
+                  }
+                }
+              },
+              "api": {
+                "type": "object",
+                "properties": {
+                  "type": {
+                    "type": "string",
+                    "example": "string"
+                  },
+                  "example": {
+                    "type": "string",
+                    "example": "v1"
+                  },
+                  "description": {
+                    "type": "string",
+                    "example": "API contract version (matches the /api/v1 mount)."
+                  }
+                }
+              },
+              "server": {
+                "type": "object",
+                "properties": {
+                  "type": {
+                    "type": "string",
+                    "example": "string"
+                  },
+                  "example": {
+                    "type": "string",
+                    "example": "1.0.0"
+                  },
+                  "description": {
+                    "type": "string",
+                    "example": "Server package version (informational)."
+                  }
+                }
               }
             }
           }

server/swagger/swagger.js

@@ -575,6 +575,16 @@ const doc = {
         properties: {
           mode: { type: 'string', enum: ['live', 'maintenance'], example: 'live' },
           status_message: { type: 'string', example: '' },
+          version: { $ref: '#/components/schemas/PublicVersion' },
+        },
+      },
+      PublicVersion: {
+        type: 'object',
+        description: 'Backend identity + version (GET /public/version; also embedded in /public/status).',
+        properties: {
+          service: { type: 'string', example: 'runic-gateway', description: 'Stable backend identifier for first-run recognition.' },
+          api: { type: 'string', example: 'v1', description: 'API contract version (matches the /api/v1 mount).' },
+          server: { type: 'string', example: '1.0.0', description: 'Server package version (informational).' },
         },
       },
       // Delete/mutation acknowledgements — each echoes the affected resource key