refactor: apply minimal tfcode branding

- Rename packages/opencode → packages/tfcode (directory only)
- Rename bin/opencode → bin/tfcode (CLI binary)
- Rename .opencode → .tfcode (config directory)
- Update package.json name and bin field
- Update config directory path references (.tfcode)
- Keep internal code references as 'opencode' for easy upstream sync
- Keep @opencode-ai/* workspace package names

This minimal branding approach allows clean merges from upstream
opencode repository while providing tfcode branding for users.

packages/tfcode/test/lib/effect.ts

@@ -0,0 +1,37 @@
+import { test, type TestOptions } from "bun:test"
+import { Cause, Effect, Exit, Layer } from "effect"
+import type * as Scope from "effect/Scope"
+import * as TestConsole from "effect/testing/TestConsole"
+
+type Body<A, E, R> = Effect.Effect<A, E, R> | (() => Effect.Effect<A, E, R>)
+const env = TestConsole.layer
+
+const body = <A, E, R>(value: Body<A, E, R>) => Effect.suspend(() => (typeof value === "function" ? value() : value))
+
+const run = <A, E, R, E2>(value: Body<A, E, R | Scope.Scope>, layer: Layer.Layer<R, E2, never>) =>
+  Effect.gen(function* () {
+    const exit = yield* body(value).pipe(Effect.scoped, Effect.provide(layer), Effect.exit)
+    if (Exit.isFailure(exit)) {
+      for (const err of Cause.prettyErrors(exit.cause)) {
+        yield* Effect.logError(err)
+      }
+    }
+    return yield* exit
+  }).pipe(Effect.runPromise)
+
+const make = <R, E>(layer: Layer.Layer<R, E, never>) => {
+  const effect = <A, E2>(name: string, value: Body<A, E2, R | Scope.Scope>, opts?: number | TestOptions) =>
+    test(name, () => run(value, layer), opts)
+
+  effect.only = <A, E2>(name: string, value: Body<A, E2, R | Scope.Scope>, opts?: number | TestOptions) =>
+    test.only(name, () => run(value, layer), opts)
+
+  effect.skip = <A, E2>(name: string, value: Body<A, E2, R | Scope.Scope>, opts?: number | TestOptions) =>
+    test.skip(name, () => run(value, layer), opts)
+
+  return { effect }
+}
+
+export const it = make(env)
+
+export const testEffect = <R, E>(layer: Layer.Layer<R, E, never>) => make(Layer.provideMerge(layer, env))

packages/tfcode/test/lib/filesystem.ts

@@ -0,0 +1,10 @@
+import path from "path"
+import { Effect, FileSystem } from "effect"
+
+export const writeFileStringScoped = Effect.fn("test.writeFileStringScoped")(function* (file: string, text: string) {
+  const fs = yield* FileSystem.FileSystem
+  yield* fs.makeDirectory(path.dirname(file), { recursive: true })
+  yield* fs.writeFileString(file, text)
+  yield* Effect.addFinalizer(() => fs.remove(file, { force: true }).pipe(Effect.orDie))
+  return file
+})