fix(xcecli): assert own hostname as FROM_HOST at submission time (bug-1676, gitea #44)

JobSubmitRequest gains a FromHost field, populated in BuildJobRequest()
via os.Hostname(). Matches how traditional batch schedulers report the
submitting host, and sidesteps having the server derive it from the
connection (which apiserver was doing via ctx.ClientIP() -- an IP not
a hostname, and spoofable via X-Forwarded-For since this apiserver
never configures gin's TrustedProxies).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01AgYRU3zDTqNGV5Jk8aiKLg

src/frontend/xcecli/cmd/jobs/submit_test.go

@@ -0,0 +1,27 @@
+package jobs
+
+import (
+	"os"
+	"testing"
+)
+
+// bug-1676: BuildJobRequest asserts our own hostname as FromHost rather than
+// leaving it for the server to derive from the connection (spoofable via
+// X-Forwarded-For, and only ever an IP, never a hostname).
+func TestBuildJobRequest_SetsFromHostToLocalHostname(t *testing.T) {
+	js := NewJobSubmitter(nil)
+	js.command = "sleep 1"
+
+	req, err := js.BuildJobRequest()
+	if err != nil {
+		t.Fatalf("BuildJobRequest: %v", err)
+	}
+
+	wantHost, hostErr := os.Hostname()
+	if hostErr != nil {
+		t.Skipf("os.Hostname() unavailable in this environment: %v", hostErr)
+	}
+	if req.FromHost != wantHost {
+		t.Errorf("FromHost = %q, want local hostname %q", req.FromHost, wantHost)
+	}
+}