* refactor(ui): consolidate dashboard to one shell in the (dashboard) layout
Moves the legacy ?page= switch page into the (dashboard) route group and
hoists Navbar, sidebar, ThemeProvider, and DebugWarningBanner into the
shared layout with real props, deleting the degraded duplicate shell that
wrapped migrated routes. The active page key now derives from the URL at
render time, so navigating between legacy and migrated pages no longer
remounts the shell.
useProxySettings becomes a React Query hook taking accessToken, shared by
the navbar, the AdminPanel arm, and migrated pages; this replaces the
lifted proxySettings state and the Navbar setProxySettings prop drilling.
The invitation onboarding flow (?invitation_id=) keeps rendering without
chrome via a layout escape hatch. Dead dark mode state and the no-op antd
ConfigProvider are removed.
* fix(ui): include accessToken in useProxySettings query key
The queryFn closes over accessToken, so the key must include it for the
cache to be honest about its inputs. Settings are instance-global today,
which made the omission harmless, but a token change while mounted would
have served the cached entry without refetching.
* test(ui): point CreateKeyPage test at the moved page
The page moved into the (dashboard) route group and no longer renders
the navbar (the layout owns chrome now), so the valid-token test asserts
the default page content (UserDashboard stub) instead.
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