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/tests/test_cli.py

@@ -712,3 +712,26 @@ def test_serve_moves_off_a_port_that_is_taken() -> None:
     assert _parser().parse_args(["serve"]).port is None
     assert _parser().parse_args(["serve", "--port", "9000"]).port == 9000
     assert DEFAULT_PORT == 8000
+
+
+def test_a_duration_reads_the_way_an_age_does() -> None:
+    """One notation for both, rather than one per place that printed one."""
+    from fluksio.sdk.cli import _dur
+
+    assert _dur(None) == "0.0s"
+    assert _dur(1240) == "1.2s"
+    assert _dur(90_000) == "1.5min"
+    # A run measured in hours used to print four digits of seconds.
+    assert _dur(7_200_000) == "2.0h"
+    assert _dur(172_800_000) == "2.0d"
+
+
+def test_the_dashboard_subscribes_where_the_browser_does() -> None:
+    """The same socket, and the token where a handshake can carry it."""
+    from fluksio.sdk.stream import socket_url
+
+    assert socket_url("http://127.0.0.1:8000", "abc") == (
+        "ws://127.0.0.1:8000/api/v1/flows/ws?token=abc"
+    )
+    # TLS on the one side is TLS on the other.
+    assert socket_url("https://engine.example.com", "t").startswith("wss://")