fix(submit): bound the untrusted upload lane — per-user caps + throttles (#75)

A logged-in user could file submissions without bound and stream a 1 GiB
context per submission. The only limits were the single-blob size cap and the
5 GiB uploads PVC (platform/workloads.go); nothing counted a user's rows or
bytes, so one account could fill the volume and every other user's upload
would start failing.

- Create: per-user pending_review cap (default 5) — the review queue cannot
  be parked full of one account's rows. Check-then-insert, documented soft.
- UploadContext: per-user stored-context budget (default 2 GiB) charged
  against the blob store's REAL sizes (new Blobs.Size on local/S3 stores), so
  the sum cannot drift from the volume; the write is capped at the remaining
  budget, so the excess is refused before it is persisted, and a re-upload is
  charged only for its new bytes.
- API: per-user create/upload throttles (30s/15s, cmd/felis-wired) on a
  dedicated cooldown keyspace, reserve→release so a failed attempt never
  burns the window and a burst collapses to one winner; ErrQuotaExceeded →
  403 submission_quota_exceeded (distinct from the 400 an oversize blob
  gets), 429 submission_cooldown for the throttles.
- Panel: zh/en copy for both codes; openapi documents 403/429 on the two
  user routes; pgint covers the pending-queue count.

Unit tests: submit package (cap, budget boundary/exact-fit/replacement,
oversize-vs-quota split) and api handlers (quota 403 both paths, throttle
429 + recovery + failure-release). go vet/go test/gofmt clean; panel
vitest 118 + typecheck green.

cmd/felis/api.go

@@ -291,6 +291,11 @@ func cmdAPI(args []string, stdout, stderr io.Writer) int {
 		AdminHostname: cfg.Auth.AdminHostname,
 		PanelHostname: cfg.Auth.PanelHostname,
 		WakeCooldown:  30 * time.Second,
+		// The user-modpack lane's per-user throttles: a create spaces out
+		// review-queue rows, an upload spaces out (up to 1 GiB) context streams.
+		// Separate keys, so the normal create→upload sequence stays immediate.
+		SubmitCreateCooldown: 30 * time.Second,
+		SubmitUploadCooldown: 15 * time.Second,
 		// Bound concurrent console/build-log SSE streams per principal. Generous enough
 		// for legitimate multi-tab / multi-server watching, while capping how many
 		// upstream follow connections a single caller can tie up if their streams stall.