Add system updates page to admin section

Add a new API endpoint and UI section for checking system updates, including internationalized locale strings and necessary dependency updates.

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lib/api-spec/openapi.yaml

@@ -30,6 +30,8 @@ tags:
     description: Object storage upload and serving endpoints
   - name: audit
     description: Admin audit log
+  - name: system
+    description: System metadata (version, update availability)
 
 paths:
   /healthz:
@@ -45,6 +47,24 @@ paths:
               schema:
                 $ref: "#/components/schemas/HealthStatus"
 
+  /system/version:
+    get:
+      operationId: getSystemVersion
+      tags: [system]
+      summary: Get current and latest system version
+      description: |
+        Returns the local build version (read from version.json embedded at
+        build time) and, if `LATEST_VERSION_URL` is configured on the
+        server, the latest published version fetched from that URL. Admin
+        only. Never performs an update — pure read.
+      responses:
+        "200":
+          description: System version info
+          content:
+            application/json:
+              schema:
+                $ref: "#/components/schemas/SystemVersionResponse"
+
   # Auth
   /auth/register:
     post:
@@ -2927,6 +2947,44 @@ components:
       required:
         - status
 
+    SystemVersionInfo:
+      type: object
+      properties:
+        version:
+          type: string
+        build:
+          type: string
+      required:
+        - version
+        - build
+
+    SystemVersionResponse:
+      type: object
+      properties:
+        current:
+          $ref: "#/components/schemas/SystemVersionInfo"
+        latest:
+          oneOf:
+            - $ref: "#/components/schemas/SystemVersionInfo"
+            - type: "null"
+        status:
+          type: string
+          enum: [up-to-date, update-available, not-configured, error]
+        errorMessage:
+          type: ["string", "null"]
+        checkedAt:
+          type: ["string", "null"]
+          format: date-time
+        configured:
+          type: boolean
+      required:
+        - current
+        - latest
+        - status
+        - errorMessage
+        - checkedAt
+        - configured
+
     ErrorResponse:
       type: object
       properties: