Move /platform/detection vars into /env (#9707)

* Add platform vars to env

* Replace /platform/detection with /env

src/state/session/index.tsx

@@ -1,10 +1,10 @@
 import React from 'react'
 import {type AtpSessionEvent, type BskyAgent} from '@atproto/api'
 
-import {isWeb} from '#/platform/detection'
 import * as persisted from '#/state/persisted'
 import {useCloseAllActiveElements} from '#/state/util'
 import {useGlobalDialogsControlContext} from '#/components/dialogs/Context'
+import {IS_WEB} from '#/env'
 import {emitSessionDropped} from '../events'
 import {
   agentToSessionAccount,
@@ -340,7 +340,7 @@ export function Provider({children}: React.PropsWithChildren<{}>) {
   )
 
   // @ts-expect-error window type is not declared, debug only
-  if (__DEV__ && isWeb) window.agent = state.currentAgentState.agent
+  if (__DEV__ && IS_WEB) window.agent = state.currentAgentState.agent
 
   const agent = state.currentAgentState.agent as BskyAppAgent
   const currentAgentRef = React.useRef(agent)