Draw curves in the terminal, and stop waiting five seconds to hear

`space` ticks runs on the serve dashboard's table and `enter` compares them:
one metric in braille, five distinct hues, and the table of what actually
differs under it. Both halves are routes that already existed — the browser's
own comparison endpoint for the curves, the runs export for the table, whose
input columns are filtered to the ones that vary.

The palette is hue rather than the web's lightness ramp on purpose: five steps
of one brand hue collapse to a single colour on a 16-colour tty.

The screen also subscribes to the engine's event bus over the same websocket a
browser uses, so a run that starts and finishes inside a tick is seen rather
than only recorded. `a` lists what a run left behind and fetches it.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_014SmyLMSqcJQ8tUL2qLj21s

backend/fluksio/sdk/client.py

@@ -390,12 +390,17 @@ class Client:
             query["name"] = name
         return self._call("GET", f"/runs/{run_id}/metrics", params=query)
 
-    def compare(self, ids: Iterable[str], metric: str) -> Any:
-        return self._call(
-            "GET",
-            "/runs/series/compare",
-            params={"ids": ",".join(ids), "metric": metric},
-        )
+    def compare(self, ids: Iterable[str], metric: str, x: str = "") -> Any:
+        """One metric across several runs, in the chart widget's series shape.
+
+        ``x`` is what the readings are plotted against: the step they were
+        recorded at, "time" for the seconds since each run's own first one, or
+        another metric of the same runs.
+        """
+        query = {"ids": ",".join(ids), "metric": metric}
+        if x:
+            query["x"] = x
+        return self._call("GET", "/runs/series/compare", params=query)
 
     def export_metrics(
         self,