feat(flows): sealed-aware flow list — hub sample flag, own dir, sample import

Three connection-truth fixes on the flow surface:

* The editor now lists the CONNECTED hub's flows: inside a sealed
  area Studio passes the instance's own flows dir
  (~/.chain/sealed/<slug>/data/flows) — previously the editor kept
  showing the shared hub's files whatever the connection, so a
  sealed area's list was simply wrong (and runSavedFlow hit the
  other hub's namespace).
* A connection switch replaces the editor state entirely (keyed by
  the sealed slug): an open buffer from one context never survives
  into the other — same privacy class as the switch race.
* Sample truth comes from the hub: listFlows' FlowSummary.sample
  (regenerated Dart SDK stubs) feeds the editor's sampleFlowNames;
  unknown (old hub / fetch failed) means no chips. Inside a sealed
  area the empty list offers the deliberate 'import example flows'
  action via chain flows import-samples against the instance's own
  dirs; the shared hub gets no such offer (it seeds samples itself,
  and a deliberate deletion is respected).

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

pubspec.lock

@@ -46,7 +46,7 @@ packages:
       path: "../fai_chain_studio_flow_editor"
       relative: true
     source: path
-    version: "0.25.0"
+    version: "0.26.0"
   characters:
     dependency: transitive
     description: