refactor(tool): convert webfetch tool internals to Effect (#21809)

packages/opencode/test/session/prompt-effect.test.ts

@@ -1,6 +1,7 @@
 import { NodeFileSystem } from "@effect/platform-node"
 import { expect } from "bun:test"
 import { Cause, Effect, Exit, Fiber, Layer } from "effect"
+import { FetchHttpClient } from "effect/unstable/http"
 import path from "path"
 import z from "zod"
 import { Agent as AgentSvc } from "../../src/agent/agent"
@@ -169,6 +170,7 @@ function makeHttp() {
   const todo = Todo.layer.pipe(Layer.provideMerge(deps))
   const registry = ToolRegistry.layer.pipe(
     Layer.provide(Skill.defaultLayer),
+    Layer.provide(FetchHttpClient.layer),
     Layer.provideMerge(todo),
     Layer.provideMerge(question),
     Layer.provideMerge(deps),