feat(api): support optional systemInfo in submissions

Extend the submission contract to accept a `systemInfo` object and persist it with each submission, including deep-copy support for `extra` metadata.

Also update client-facing docs and HTTP examples (JSON and multipart) and document that the schema is available at `GET /api/schema`, so clients can reliably implement the updated payload format.feat(api): support optional systemInfo in submissions

Extend the submission contract to accept a `systemInfo` object and persist it with each submission, including deep-copy support for `extra` metadata.

Also update client-facing docs and HTTP examples (JSON and multipart) and document that the schema is available at `GET /api/schema`, so clients can reliably implement the updated payload format.

http/submit-json.http

@@ -4,6 +4,16 @@ Content-Type: application/json
 {
   "submitter": "Workstation-Lab-A",
   "platform": "windows",
+  "systemInfo": {
+    "hostname": "workstation-lab-a",
+    "osName": "Windows",
+    "osVersion": "11 24H2",
+    "kernelVersion": "10.0.26100",
+    "architecture": "amd64",
+    "locale": "en-US",
+    "timezone": "Europe/Bucharest",
+    "clientVersion": "1.0.0"
+  },
   "benchmark": {
     "config": {
       "durationSecs": 20,

http/submit-multipart.http

@@ -10,6 +10,10 @@ Content-Disposition: form-data; name="platform"
 
 linux
 --BenchBoundary
+Content-Disposition: form-data; name="systemInfo"
+
+{"hostname":"intel-test-rig","osName":"Ubuntu","osVersion":"24.04","kernelVersion":"6.8.0-58-generic","architecture":"amd64","locale":"en-US","timezone":"Europe/Bucharest","clientVersion":"1.0.0"}
+--BenchBoundary
 Content-Disposition: form-data; name="benchmark"; filename="cpu-bench-result.json"
 Content-Type: application/json