feat(job-array-one-based-index): REST submit creates arrays numbered from 1 (task 6.2)

preCheckJobRequest returns (n, isArray, err): a bracketed job name is
parsed by ParseSubmitIndexExpr first, so name[1-N] and name[1] create
arrays (one-element arrays included) allocated with
generateArrayJobID, stored under the bare name; expression errors are
answered 400 with their specific message and create nothing; names
without brackets take the unchanged createArrayName path. The response
names the array (jobid = array ID, new array_size, "(n elements)"),
submit-time %I/%J use the first element, and the submit and dispatch
logs identify arrays by array ID. Fixes bug-1896 for REST and xcecli.

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

src/frontend/apiserver/models/jobs.go

@@ -710,6 +710,9 @@ type JobSubmitResponse struct {
 	JobID     int64  `json:"jobid"`
 	QueueName string `json:"queue_name"`
 	Message   string `json:"message"`
+	// ArraySize is the number of elements of a submitted array; omitted
+	// for an ordinary job (3.2, 3.3).
+	ArraySize int `json:"array_size,omitempty"`
 }
 
 // Job query struct in C lib