fix: use cmd.Context() instead of context.Background()

[dgageot]

During an audit of context.Background() usage in the codebase, this was identified as the one genuinely suspicious instance. The shell-completion handler for completeMessage was passing context.Background() to config.Load(), which meant completion operations ignored the cobra command's own context and could not be cancelled or respect deadline constraints.

This change passes cmd.Context() instead, ensuring that shell completion respects cancellation and any deadlines set by the caller. The now-unused context import was removed.

All other context.Background() occurrences in the codebase were reviewed and deemed intentional (detached long-lived resources, sync.Once caches, fire-and-forget calls), so no further changes are needed.

[docker-agent]

Assessment: 🟢 APPROVE

This is a clean, well-scoped fix. The change correctly replaces context.Background() with cmd.Context() in the completeMessage shell-completion handler.

Analysis:

• cmd.Context() in Cobra always returns a non-nil context (falls back to context.Background() if none is explicitly set), so this is strictly safer than a bare context.Background().
• The existing error handling (return nil, cobra.ShellCompDirectiveNoFileComp on config.Load error) already handles any context-cancellation-driven errors gracefully.
• The context import removal is correct — no other usages of the context package remain in the file.
• The change is minimal, targeted, and correct. No bugs were found.