fix(ui): restore classic padding on Astryx dialog headers

[cijiugechu]

Summary

Closes #1713.

The Astryx modal migration (#1674) dropped the dialog header inset and
the follow-up adapter removal (#1688) moved padding={0} into the five
dialog call sites. Astryx's DialogHeader derives its padding from the
dialog container's --layout-padding-* variables, so with padding={0}
the provider icon, title, subtitle and close button render flush against
the modal edges in every dialog.

This removes padding={0} from the five <Dialog> call sites
(provider connection, bot onboarding, WeChat QR, MCP editor, keyboard
help). The header now picks up the Astryx theme default
(--astryx-dialog-padding, 16px).

Why call sites instead of a shared default: #1688 removed the
@maka/ui compatibility layer, so the padding decision now lives at
the call sites — there is no adapter left to fix. Each dialog keeps
LayoutContent padding={0} and its own body inset, so no body spacing
changes; scoping the fix to the header leaves every other inset
identical.

Verification

• npm run lint — clean (2423 files)
• npm run format:check — clean (1321 files)
• npm run typecheck — all 10 workspaces pass.
• npm --workspace @maka/ui run build — pass

[Astro-Han]

Reviewed the current head. Removing the five local padding overrides restores the Astryx dialog-header inset while leaving body padding, scrolling, and focus behavior unchanged. I found no issues in the patch.

GitHub checks have not run for this PR, so this approval covers the diff only. Please run the required checks before merge.