feat(studio): typed run-flow form, file picker, copyable errors (v0.41.0)

The free-form key=value run-flow dialog produced two
unhelpful failures every time an operator hit Run:

  1. Submit empty → "step references missing value
     '\$inputs.document'" from the hub. Studio sent a zero-
     entry inputs map because nothing told the operator the
     flow declared a required input.
  2. Type `document=@/path/to/file` → "path not found".
     Dart's `File()` doesn't expand `~`, and on macOS
     sandboxed Studio can't read arbitrary paths anyway.

Both failure modes are gone. The dialog is now a typed form:

- On open, fetches `getFlowDefinition(name)` (new SDK
  v0.15.0 wrapper around the v0.10.89 hub RPC). While that
  resolves, a small spinner shows
  "Loading inputs…"; on failure, an inline `FaiErrorBox`
  with the exact RPC error and a copy button replaces the
  spinner.
- Renders one form-field per declared input. The flow
  YAML's verbatim type tag drives the widget choice:
  `bytes` / `file` → "Choose file…" button + picked-file
  readout, plain TextField for everything else. The type
  tag is shown next to the input name as a pill so a flow
  author who picks a less-common type still gets a hint.
- Bytes inputs route through `file_picker` with
  `withData: true`, which means the OS file dialog handles
  read access — sandboxed Studio gets the bytes inline
  rather than a path it can't open. Falls back to
  `File(path).readAsBytes()` on Linux configs that don't
  honour `withData` for large files; failures show a
  copyable SnackBar.
- The Run button enables only when every declared input has
  a value (text non-empty / file picked). Empty submission
  is impossible; the cryptic hub-side
  "missing value" error stops surfacing.
- The run-result dialog's error path uses `FaiErrorBox`
  instead of the previous plain `SelectableText`, so any
  hub-side flow error (permission denied, module crash,
  whatever) is one click to clipboard.

11 new ARB keys cover the form's labels, the file-picker
states, the loading / failed-definition messages, the
"This flow declares no inputs" empty state, and the
run-error dialog title.

`file_picker: ^8.0.0` added to pubspec.yaml.

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

lib/l10n/app_localizations.dart

@@ -1823,14 +1823,62 @@ abstract class AppLocalizations {
   /// No description provided for @flowsRunDialogBody.
   ///
   /// In en, this message translates to:
-  /// **'Inputs as key=value, one per line. Plain values send as text. Prefix the value with `@` to read a file as bytes — same as `fai run --input document=@/path/to/file.pdf`.'**
+  /// **'One field per declared input. Pick a file for bytes-shaped inputs; type plain text for the rest. The Run button enables when every required input is set.'**
   String get flowsRunDialogBody;
 
-  /// No description provided for @flowsInputsHint.
+  /// No description provided for @flowsLoadingDefinition.
   ///
   /// In en, this message translates to:
-  /// **'name=World\ndocument=@/Users/me/Documents/sample.pdf\nstyle=three bullet points'**
-  String get flowsInputsHint;
+  /// **'Loading inputs…'**
+  String get flowsLoadingDefinition;
+
+  /// No description provided for @flowsDefinitionFailed.
+  ///
+  /// In en, this message translates to:
+  /// **'Could not load flow definition'**
+  String get flowsDefinitionFailed;
+
+  /// No description provided for @flowsNoInputs.
+  ///
+  /// In en, this message translates to:
+  /// **'This flow declares no inputs. Click Run to start.'**
+  String get flowsNoInputs;
+
+  /// No description provided for @flowsTypeBytesPick.
+  ///
+  /// In en, this message translates to:
+  /// **'Choose file…'**
+  String get flowsTypeBytesPick;
+
+  /// No description provided for @flowsTypeBytesChange.
+  ///
+  /// In en, this message translates to:
+  /// **'Change file'**
+  String get flowsTypeBytesChange;
+
+  /// No description provided for @flowsTypeBytesNoFile.
+  ///
+  /// In en, this message translates to:
+  /// **'No file selected'**
+  String get flowsTypeBytesNoFile;
+
+  /// No description provided for @flowsTypeBytesSize.
+  ///
+  /// In en, this message translates to:
+  /// **'{n} bytes'**
+  String flowsTypeBytesSize(int n);
+
+  /// No description provided for @flowsRunErrorTitle.
+  ///
+  /// In en, this message translates to:
+  /// **'Flow run failed'**
+  String get flowsRunErrorTitle;
+
+  /// No description provided for @flowsFileReadFailed.
+  ///
+  /// In en, this message translates to:
+  /// **'Could not read \"{path}\": {error}'**
+  String flowsFileReadFailed(String path, String error);
 
   /// No description provided for @flowsRunButton.
   ///