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/l10n/app_de.arb

@@ -389,8 +389,8 @@
   "flowsNoneHint": "Flow speichern mit `fai admin flows save <name> <flow.yaml>`, dann taucht er hier auf.",
   "flowsRunDialogTitle": "{name} ausführen",
   "@flowsRunDialogTitle": { "placeholders": { "name": { "type": "String" } } },
-  "flowsRunDialogBody": "Eingaben als key=value, eine pro Zeile. Alle Werte werden als Text-Payloads gesendet. Für binäre Eingaben die `fai run` CLI nutzen.",
-  "flowsInputsHint": "name=World\ntarget_language=English\nsummary_style=three bullet points",
+  "flowsRunDialogBody": "Eingaben als key=value, eine pro Zeile. Klartext-Werte landen als Text. Wert mit `@` voranstellen liest die Datei als Bytes — wie `fai run --input document=@/pfad/zu/datei.pdf`.",
+  "flowsInputsHint": "name=Welt\ndocument=@/Users/ich/Dokumente/beispiel.pdf\nstil=drei Stichpunkte",
   "flowsRunButton": "Starten",
   "flowsRunningTitle": "{name} läuft",
   "@flowsRunningTitle": { "placeholders": { "name": { "type": "String" } } },