The login page is the operator's entry point — it should look the
same every time, not flip between light and dark depending on what
the previous session left in localStorage.
Adds the `dark` class to the login wrapper div instead of
documentElement, so:
- Skyrise's .dark tokens cascade into all descendants (CSS vars defined
under .dark apply to the subtree).
- After sign-in and navigation, the user's saved light/dark preference
takes back over for the rest of the app.
Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>
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