Keep passkey prompt visible to show success feedback

[rzueger]

Summary

Fixes a bug where the post-login passkey tile disappeared immediately after successful registration — the user never saw the success confirmation that #713 added.

Root cause

The register saga fires two actions in sequence:

1. registerPasskeySuccess → state.auth.passkeyRegistration.submitting goes false
2. loadPasskeys → state.auth.passkeys populates with the new credential

The PostLoginPasskeyPromptContainer computes show as:

__CONF__.passkeysEnabled && isRealUser && passkeys.length === 0

As soon as (2) lands, show flips to false. In the component render, the if (!show || dismissed) return null gate ran before the if (showSuccess) branch, so the component returned null the moment registration succeeded. The showSuccess effect did set the state, but the success card was never rendered.

Fix

Re-order the render checks:

1. if (dismissed) return null — preserves the 3.5s auto-dismiss behaviour
2. if (showSuccess) → render success card (regardless of show)
3. if (!show) return null — normal gate for the idle state
4. Normal supported check
5. Render the main prompt

Test plan

• 1933 tests pass, typecheck clean (includes new regression test simulating the real redux sequence: submitting → false AND show → false in the same transition)
• Manually register a passkey from the tile on lszm-test
• Confirm the success card appears with the message and auto-dismisses after ~3.5s