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/pages/welcome.dart

@@ -819,8 +819,17 @@ class _DocReaderSheetState extends State<_DocReaderSheet> {
     final fallback = 'assets/docs/${widget.entry.slug}.md';
     try {
       return await rootBundle.loadString(localised);
-    } catch (_) {
-      return rootBundle.loadString(fallback);
+    } catch (firstErr) {
+      try {
+        return await rootBundle.loadString(fallback);
+      } catch (secondErr) {
+        // Surface BOTH attempted paths and the underlying
+        // errors so the operator can copy a useful diagnostic
+        // out of FaiErrorBox without us having to ship a doc
+        // about reading Flutter asset errors.
+        throw 'tried "$localised": $firstErr\n'
+            'then "$fallback": $secondErr';
+      }
     }
   }
 
@@ -887,11 +896,22 @@ class _DocReaderSheetState extends State<_DocReaderSheet> {
                 if (snap.hasError) {
                   return Padding(
                     padding: const EdgeInsets.all(FaiSpace.xxl),
-                    child: Text(
-                      l.welcomeDocFailedToLoad(snap.error.toString()),
-                      style: theme.textTheme.bodyMedium?.copyWith(
-                        color: theme.colorScheme.error,
-                      ),
+                    child: Column(
+                      crossAxisAlignment: CrossAxisAlignment.start,
+                      children: [
+                        Text(
+                          l.welcomeDocFailedToLoad(''),
+                          style: theme.textTheme.bodyMedium?.copyWith(
+                            color: theme.colorScheme.error,
+                          ),
+                        ),
+                        const SizedBox(height: FaiSpace.sm),
+                        FaiErrorBox(
+                          text: snap.error.toString(),
+                          isError: true,
+                          maxHeight: 200,
+                        ),
+                      ],
                     ),
                   );
                 }