init: arcadia-admin — admin webapp for arcadia-core, cloned from vibespace

Initial commit. Spun up via the docs/STARTER.md recipe: cp from vibespace,
reset git, rename package, set brand to "Arcadia Admin" with Shield icon
in app/lib/identity.ts.

Inherits the full Crema sibling-lib wiring including @crema/arcadia-client
(typed HTTP + Phoenix Channels realtime against arcadia-core) and
@crema/arcadia-auth-ui (login/signup/password-reset/2FA forms). The /login
route already renders <LoginForm>; <ArcadiaProvider> in app/root.tsx reads
VITE_ARCADIA_URL (default localhost:4000) and VITE_ARCADIA_TENANT (default
"default").

CLAUDE.md and README rewritten to frame this as the admin app for
arcadia-core. docs/STARTER.md removed — arcadia-admin is a leaf consumer,
not a downstream starter.

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

app/components/README.md

@@ -0,0 +1,31 @@
+# components/
+
+Component layers in this project.
+
+```
+ui/          shadcn primitives — token-driven, reskinnable per design system
+forms/       composed form widgets
+data/        data display (tables, filters, empty states)
+layout/      app shell, page chrome, navigation wrappers
+marketing/   landing and marketing blocks
+[system]/    design-system-specific components (e.g. m3/, apple/)
+```
+
+## The one rule
+
+**Custom components import *from* `ui/`, never the reverse.**
+
+`ui/` is the primitive layer. It must stay reskinnable by swapping tokens in
+`app/themes/*.css` alone. If a component can't be expressed that way (M3
+ripple, Apple segmented control, etc.), it belongs in a system-specific
+folder — not `ui/` and not the shared folders above.
+
+## Tokens, not values
+
+Every custom component should reference semantic tokens:
+
+- Colors: `bg-primary`, `text-muted-foreground`, `border-border`
+- Radius: `rounded-md`, `rounded-lg`
+- Fonts: `font-sans`, `font-heading`
+
+Hardcoded hex, oklch, or px values are a bug — they break theming.