Stage caching for batch runs, and an engine that lives in the command

A code node in a batch run is now fingerprinted by its source, its raw
settings and the values it reads — an artifact input counting as its digest,
which is what the content addressing was always for. A run that finds the key
restores what the earlier one returned and skips the node, recorded as
`cached`. The run history is the cache: `run_node.outputs` beside the
`cache_key` the schema already had, no second store. On for code nodes, never
for the built-in and connector types that have side effects; off per node with
`@node(cache=False)` and per run with `--no-cache`.

Emissions are not replayed on a hit, so a cached training node returns its
result without redrawing its curve. Recorded in NOTEPAD.md with the two other
deliberate limits.

`fluksio run --local` boots the real app in the command's own process and
drives it through its ASGI interface behind the ordinary client, so a run no
longer needs a `serve` terminal beside it — same data directory, same history,
and the cache carries between the two. It always waits, because the engine it
starts lives exactly as long as the command.

Also: `fluksio sweep --param lr=0.1,0.01` for the product of the lists,
`run --follow` for a run's numbers as they arrive, Ctrl-C cancelling a waited
run rather than abandoning it, coloured statuses on a terminal, and `name`
made optional on the metrics endpoint so a follower can ask for every series.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/code/api.md

@@ -102,12 +102,12 @@ published to. Flows own the namespace; everything else is a client of it.
 
 | Method | Path | What |
 |---|---|---|
-| `POST` | `/runs/flows/{name}` | queue one run — `{"params": {...}, "seed": 7, "draft": false}` |
+| `POST` | `/runs/flows/{name}` | queue one run — `{"params": {...}, "seed": 7, "draft": false, "no_cache": false}` |
 | `POST` | `/runs/flows/{name}/sweep` | queue many, sharing a `group_id` |
 | `GET` | `/runs` | the queryable history: `?flow=`, `?status=`, `?group=`, `?digest=`, `?limit=` |
 | `GET` | `/runs/{id}` | one run in full: params, result, per-node record, artifacts |
 | `POST` | `/runs/{id}/cancel` | stop it |
-| `GET` | `/runs/{id}/metrics?name=&stride=` | one metric's series, in step order |
+| `GET` | `/runs/{id}/metrics?name=&stride=` | one metric's series, in step order; every series of the run without `name` |
 | `GET` | `/runs/series/compare?ids=a,b,c&metric=` | that metric across several runs |
 
 Submitting answers immediately with a `queued` run. Wrong parameters — an