Every panel page CSS file repeated the same wrapper boilerplate — the
--bg-page/--bg-card token triples for light/dark/ultra-dark, the
min-height + background root rule, the .ant-layout transparent reset,
the .content-shell transparent reset, and the .loading-spacer min-height.
That's ~30 identical lines duplicated across IndexPage, ClientsPage,
InboundsPage, XrayPage, SettingsPage, NodesPage, and ApiDocsPage.
Move all of it into styles/page-shell.css and import it once from
main.tsx alongside utils.css and page-cards.css. Each page CSS file
now only contains genuinely page-specific rules (content-area padding
overrides, page-specific tokens like ApiDocs's Swagger --sw-* set).
Also drop the per-page `import '@/styles/page-cards.css'` statements
from the 7 page tsx files now that main.tsx loads it globally.
Net: -211 deleted, +6 inserted in the touched files, plus the new
page-shell.css. .zero-margin (Divider override used by Nord/Warp
modals) folded into utils.css alongside the margin classes.
