fix(dialog): synchronize native modal activation

[Banegasn]

Summary\n- activate the native dialog top-layer state during Lit's post-render open update\n- retain deferred initial focus for slotted component rendering\n- verify stacked dialogs are natively open after their open update\n\n## Verification\n- (Chromium, Firefox, WebKit)\n- \n-

[Banegasn]

Acceptance review found a P1 reconnect regression: an open dialog is deactivated/closed natively on disconnect but retains open=true; on reconnect it restores stack/inert state without reopening the native modal because open has not changed. Restore native activation after the rendered reconnect path and add a remove/reappend open-dialog regression asserting native .open/top-layer modal behavior. Implementation has been returned for this focused correction.