Document progress suppression for sandbox runs (#26498)

Document `sbx run --no-progress` in the CI and headless guide so scripts
can suppress creation progress while retaining command results,
including detached sandbox IDs.

Validation: Markdown formatting and scoped rumdl/Vale lint passed.
Implementation and regression tests were reviewed; test execution was
blocked by the installed Go version.

content/manuals/ai/sandboxes/workflows/automation.md

@@ -99,6 +99,9 @@ For lists of identifiers without table headings, use `--quiet` or `-q`:
 | `sbx settings ls -q` | Setting keys. |
 | `sbx policy approval ls -q` | Approval IDs. |
 
+To suppress sandbox creation progress, use `sbx run --no-progress`. Command
+results are still printed, including the sandbox ID when you use `--detach`.
+
 ### Update scripts for v0.48.0
 
 {{< copy-as-prompt instruction="Update this repository's Docker Sandboxes CLI usage for v0.48.0 using the migration reference below. Inspect scripts and documentation, update affected commands and output parsers, and verify the changes. Preserve unrelated behavior." >}}