refactor(file): effectify FileService as scoped service

Convert File namespace functions (init, status, read, list, search) to
FileService class extending ServiceMap.Service with Effect.fn methods.
File cache uses lazy initialization via init() matching original
Instance.state semantics. Legacy promise facade preserved.

packages/opencode/src/effect/instances.ts

@@ -8,6 +8,7 @@ import { FileWatcherService } from "@/file/watcher"
 import { VcsService } from "@/project/vcs"
 import { FileTimeService } from "@/file/time"
 import { FormatService } from "@/format"
+import { FileService } from "@/file"
 import { Instance } from "@/project/instance"
 
 export { InstanceContext } from "./instance-context"
@@ -20,6 +21,7 @@ export type InstanceServices =
   | VcsService
   | FileTimeService
   | FormatService
+  | FileService
 
 function lookup(directory: string) {
   const project = Instance.project
@@ -32,6 +34,7 @@ function lookup(directory: string) {
     Layer.fresh(VcsService.layer),
     Layer.fresh(FileTimeService.layer).pipe(Layer.orDie),
     Layer.fresh(FormatService.layer),
+    Layer.fresh(FileService.layer),
   ).pipe(Layer.provide(ctx))
 }