feat(studio): live step-progress in flow-run dialog

The flow-run dialog showed a single spinner + "running…" label
for the whole run. For multi-step flows the operator had no
way to see *which* step was busy or how close the run was to
finishing.

Replace the spinner with a live step list driven by a
StreamEvents subscription:

  ✔ extract       0.41s
  ⏳ summarize
  ◻ notify
  ━━━━━━━━━━────  35%

Mirrors the `fai run` CLI rendering — one shared visual
language across both surfaces. Steps appear in execution
order as the hub emits step.started events; check + duration
on completion; cross + first-line error on failure; pause
icon on approval gates.

Implementation:

 - HubService.streamEvents(backfill, types) — new public
   stream-facade method that wraps HubClient.streamEvents and
   maps proto LoggedEvent → AuditEvent for the rest of Studio.
   Subscribed with backfill=0 so the dialog only sees events
   from this very run.

 - _FlowRunDialogState.initState subscribes BEFORE submitting
   the run, so the first step.started never gets lost in the
   gRPC handshake gap.

 - Two-layer filter on incoming events: same flow name AND
   timestamp >= dialog open time. The timestamp gate is what
   stops a previous run's tail-end from painting stale rows
   if the user re-runs the same saved flow.

 - _LiveStep + _LiveStepList — insertion-ordered map renders
   rows in runtime execution order (not alphabetical), so
   what the operator sees matches what the hub did.

Version 0.51.5 → 0.51.6.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

pubspec.yaml

@@ -1,7 +1,7 @@
 name: fai_studio
 description: "F∆I Studio — desktop GUI for the F∆I hub"
 publish_to: 'none'
-version: 0.51.5
+version: 0.51.6
 
 environment:
   sdk: ^3.11.0-200.1.beta