feat(studio): @-syntax file inputs in flows, copyable doc errors, services-row overflow (v0.40.0)

Three concrete fixes against today's user feedback.

- Flows that take binary inputs (extract / extract-summarize /
  …) work from the Flows tab. The run-flow input dialog now
  accepts the same `@/path/to/file` syntax `fai run --input`
  uses on the CLI: any value beginning with `@` is read as
  bytes and sent as a binary Payload; plain values still flow
  through as text. The dialog hint copy and the example
  placeholder reflect the new syntax. File-read failures
  surface as a SnackBar before the run dialog opens, so a
  typo in the path doesn't reach the hub. Threaded through
  `_FlowRunDialog` and `HubService.runSavedFlow`, which both
  carry separate `textInputs` and `fileInputs` maps now and
  forward to the SDK's mixed-mode runSavedFlow (v0.14.0).

- The Welcome doc-reader's error path uses `FaiErrorBox` so
  the actual underlying error is selectable + copy-to-
  clipboard via the existing widget. Plus the loader throws
  a richer error string that names *both* attempted asset
  paths (`<slug>_<lang>.md` and the EN fallback) and the
  underlying exception each, so the operator can paste a
  diagnostic into a chat without us having to ship a
  separate "how to read Flutter asset errors" doc.

- Doctor's empty Services panel had a horizontal RenderFlex
  overflow at narrow widths because the long mono-spaced
  hint ("add to ~/.fai/config.yaml under services:") and
  the leading icon+text both demanded full intrinsic width
  in a single Row. Now wraps via a `Wrap` widget so the
  hint flows to a second line on narrow viewports and stays
  in the same row when there's space.

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

lib/data/hub.dart

@@ -5,6 +5,8 @@
 // Methods return UI-friendly types so pages stay free of
 // protobuf imports.
 
+import 'dart:typed_data';
+
 import 'package:fai_dart_sdk/fai_dart_sdk.dart';
 import 'package:flutter/widgets.dart';
 import 'package:shared_preferences/shared_preferences.dart';
@@ -544,15 +546,20 @@ class HubService {
       ..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.
+  /// Run a saved flow with the supplied inputs. Text values
+  /// land as text Payloads, byte values as bytes Payloads —
+  /// flows that mix both (e.g. extract taking a `document:
+  /// bytes` plus a text-shaped option) flow through one RPC.
+  /// Returns the named outputs as a map of UI-friendly strings.
   Future<Map<String, String>> runSavedFlow({
     required String name,
-    required Map<String, String> textInputs,
+    Map<String, String> textInputs = const {},
+    Map<String, Uint8List> fileInputs = const {},
   }) async {
     final r = await _client.runSavedFlow(
       name: name,
       textInputs: textInputs,
+      fileInputs: fileInputs,
     );
     return {
       for (final entry in r.outputs.entries)