refactor(auth): remove unused SessionProvider wrapper

Remove the passthrough AuthSessionProvider component and its usage
in layout. better-auth hooks work without a provider wrapper.

src/components/SessionProvider.tsx

@@ -1,11 +0,0 @@
-"use client"
-
-import { ReactNode } from "react"
-
-interface Props {
-  children: ReactNode
-}
-
-export default function AuthSessionProvider({ children }: Props) {
-  return <>{children}</>
-}