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/doctor.dart

@@ -734,22 +734,32 @@ class _ServicesPanel extends StatelessWidget {
     final theme = Theme.of(context);
     final l = AppLocalizations.of(context)!;
     if (snapshot.services.isEmpty) {
+      // Wrap on narrow windows so the mono-spaced hint
+      // (`add to ~/.fai/config.yaml under services:`) does not
+      // overflow horizontally past the card's right edge.
       return FaiCard(
-        child: Row(
+        child: Wrap(
+          spacing: FaiSpace.sm,
+          runSpacing: FaiSpace.xs,
+          crossAxisAlignment: WrapCrossAlignment.center,
           children: [
-            Icon(
-              Icons.dns_outlined,
-              size: 18,
-              color: theme.colorScheme.onSurfaceVariant,
+            Row(
+              mainAxisSize: MainAxisSize.min,
+              children: [
+                Icon(
+                  Icons.dns_outlined,
+                  size: 18,
+                  color: theme.colorScheme.onSurfaceVariant,
+                ),
+                const SizedBox(width: FaiSpace.sm),
+                Text(
+                  l.doctorServicesEmpty,
+                  style: theme.textTheme.bodyMedium?.copyWith(
+                    color: theme.colorScheme.onSurfaceVariant,
+                  ),
+                ),
+              ],
             ),
-            const SizedBox(width: FaiSpace.sm),
-            Text(
-              l.doctorServicesEmpty,
-              style: theme.textTheme.bodyMedium?.copyWith(
-                color: theme.colorScheme.onSurfaceVariant,
-              ),
-            ),
-            const Spacer(),
             Text(
               l.doctorServicesEmptyHint,
               style: FaiTheme.mono(