ai: scope console theme to content wrapper, fix font loading

Two bugs in the previous /ai redesign:

1. theme="console" on AppShell put the entire shell (sidebar, appbar,
   appbar dropdowns, the lot) inside [data-theme="console"], so the
   console palette + JetBrains Mono override leaked into the sidebar
   and made light mode look broken on /ai. Scoped now: the AppShell
   stays in skyrise (so light/dark toggle keeps working everywhere),
   and only the route content area gets data-theme="console" via an
   inner wrapper.

2. The Google Fonts @import inside console.css was being silently
   dropped because @import rules must precede all other rules in the
   final bundle, and skyrise's content lands first. Moved JetBrains
   Mono + Newsreader into app.css's top-level @import url() alongside
   the existing Inter/Instrument Sans/Geist Mono families.

Atmosphere ::before was also position: fixed, which painted the grain
overlay across the whole viewport (including the sidebar) regardless
of where data-theme lived. Now position: absolute on the wrapper, with
isolation: isolate to keep z-index local.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/app.css

@@ -1,4 +1,4 @@
-@import url("https://fonts.googleapis.com/css2?family=Inter:ital,opsz,wght@0,14..32,100..900;1,14..32,100..900&family=Instrument+Sans:ital,wght@0,400..700;1,400..700&family=Geist+Mono:wght@100..900&display=swap");
+@import url("https://fonts.googleapis.com/css2?family=Inter:ital,opsz,wght@0,14..32,100..900;1,14..32,100..900&family=Instrument+Sans:ital,wght@0,400..700;1,400..700&family=Geist+Mono:wght@100..900&family=JetBrains+Mono:ital,wght@0,400;0,500;0,600;0,700;1,400&family=Newsreader:ital,opsz,wght@0,6..72,400;0,6..72,500;0,6..72,600;1,6..72,400&display=swap");
 
 /* Active theme — must be first so its @import url() font directives resolve
  * to the top of the output. Themes are self-contained: tokens + fonts. */