feat(ui): Flows page (5th destination) + keyboard shortcuts

Two operator-DX additions:

1. **Flows** is the new third destination in the sidebar.
   Lists saved flows from the hub via the new HubAdmin
   ListFlows RPC. Each row has a Run button that opens an
   input dialog (key=value pairs, one per line, all values
   sent as text payloads — the binary-input case stays in
   `fai run` CLI). Flow runs in a non-dismissable progress
   dialog; output is shown per-key with monospace
   selectable text. Errors render with the exception detail
   for diagnosis.

2. **Keyboard shortcuts** at the shell level:
   - Cmd+1 / Cmd+2 / Cmd+3 / Cmd+4 / Cmd+5 jump to the
     matching destination (Doctor / Modules / Flows / Audit
     / Approvals).
   - Cmd+, opens the Settings dialog (macOS convention).

   Implemented via Flutter's Shortcuts/Actions/Intent triple
   so the bindings are discoverable in IDE devtools and
   composable with platform-specific overrides later.

Bumps fai_studio 0.7.3 -> 0.8.0.

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

lib/data/hub.dart

@@ -106,6 +106,49 @@ class HubService {
     );
   }
 
+  /// Saved flows known to the hub.
+  Future<List<SavedFlow>> listFlows() async {
+    final flows = await _client.listFlows();
+    return flows
+        .map(
+          (f) => SavedFlow(
+            name: f.name,
+            path: f.path,
+            sizeBytes: f.sizeBytes.toInt(),
+          ),
+        )
+        .toList()
+      ..sort((a, b) => a.name.compareTo(b.name));
+  }
+
+  /// Run a saved flow with the supplied text inputs. Returns
+  /// the named outputs as a map of UI-friendly strings.
+  Future<Map<String, String>> runSavedFlow({
+    required String name,
+    required Map<String, String> textInputs,
+  }) async {
+    final r = await _client.runSavedFlow(
+      name: name,
+      textInputs: textInputs,
+    );
+    return {
+      for (final entry in r.outputs.entries)
+        entry.key: _payloadToText(entry.value),
+    };
+  }
+
+  String _payloadToText(Payload p) {
+    if (p.hasText()) return p.text;
+    if (p.hasJson()) return p.json.toString();
+    if (p.hasBytes()) {
+      return '<bytes: ${p.bytes.data.length} bytes, ${p.bytes.mimeType}>';
+    }
+    if (p.hasFile()) {
+      return '<file: ${p.file.uri}>';
+    }
+    return '<unknown payload variant>';
+  }
+
   Future<List<AuditEvent>> recentEvents({
     int limit = 50,
     List<String> types = const [],
@@ -264,6 +307,18 @@ class ModuleSummary {
   });
 }
 
+class SavedFlow {
+  final String name;
+  final String path;
+  final int sizeBytes;
+
+  const SavedFlow({
+    required this.name,
+    required this.path,
+    required this.sizeBytes,
+  });
+}
+
 class ModuleDetail {
   final String name;
   final String version;