fix(CONTRACT): add set.outflow row — registered topic was missing

Registry's `set.outflow` (alias `q_out`) pushes a measured outflow into
the basin balance. CONTRACT.md documented `set.inflow` but not its
outflow twin; contract-verify required both.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

CONTRACT.md

@@ -12,6 +12,7 @@ Hand-maintained for Phase 2; the `## Inputs` table is generated from
 | `cmd.calibrate.volume` | `calibratePredictedVolume` | numeric (number or numeric string) — m³ | Resets the predicted-volume series and seeds it with the supplied value; recomputes level. |
 | `cmd.calibrate.level` | `calibratePredictedLevel` | numeric — metres | Resets the predicted-level series and seeds it with the supplied value; recomputes volume. |
 | `set.inflow` | `q_in` | number, numeric string, or `{ value, unit, timestamp }` | Pushes a manual inflow measurement onto the predicted-flow series. `unit` may be on the message (`msg.unit`) or inside the object payload. |
+| `set.outflow` | `q_out` | number, numeric string, or `{ value, unit, timestamp }` | Pushes a measured outflow value into the basin balance. Same payload conventions as `set.inflow`. |
 | `set.demand` | `Qd` | numeric — child setpoint demand | Forwards the demand to direct children (machineGroups / machines / stations). Only honoured in `manual` mode; in other modes the call is logged at `debug` and discarded. |
 
 Aliases log a one-time deprecation warning the first time they fire.