feat(commands): route data.flow through the registry unit normaliser; wiki sync

- data.flow: declare unit:'m3/h' (payloadSchema any) and drop the handler's own
  convert() call — the registry now converts any number/string/{value,unit} to
  m3/h before the handler. Handler reads the normalised scalar.
- Regenerate wiki topic-contract.

data.flow integration test green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

wiki/Reference-Contracts.md

@@ -23,7 +23,7 @@ The registry lives in `src/commands/index.js`. Each descriptor maps a canonical
 | `cmd.start` | `i_start` | any | — | Trigger / release the sampler start gate. |
 | `set.schedule` | `monsternametijden` | any | — | Replace the sampling-times schedule. |
 | `set.rain` | `rain_data` | any | — | Push current rain-event data into the sampler logic. |
-| `data.flow` | `input_q` | `object` | — | Push the upstream flow measurement (payload: {value, unit}). |
+| `data.flow` | `input_q` | any | `volumeFlowRate` (default `m3/h`) | Push the upstream flow measurement (payload: number or {value, unit}). |
 | `set.mode` | `setMode` | any | — | Switch the monster between auto / manual modes. |
 | `set.model-prediction` | `model_prediction` | any | — | Push the upstream rain-prediction snapshot used by the sampler. |
 | `child.register` | `registerChild` | `string` | — | Register a child node (typically a measurement) with this monster. |