fix(cli): read stdin on demand (CLI-2223) (#6450)

## TL;DR

 follow-up to #6290 Piped answers past the 1024th line were dropped. 
stdin is now read one chunk at a time as prompts ask for it, so nothing
is dropped and the rest stays in the pipe...

## what was biting?

Bun reads a pipe as fast as it fills and cannot be paused, so #6290
drained it into a queue of 1024 lines to stop
 `yes | supabase db push` from eating memory. 
Anything past 1024 lines fell off the queue and those prompts took their
default...

## why this approach is better? 

A file stream over fd 0 honours backpressure, so there is no queue and
no cap.
Memory is bounded the same way Go's `bufio.Scanner` did it: a line over
64 KiB ends line reading and every prompt from then on takes its
default...

## ref:
- adds onto issue: #6287
- extends: #6290

Author: 7ttp

apps/cli/src/legacy/commands/encryption/update-root-key/update-root-key.command.ts

@@ -1,4 +1,3 @@
-import { BunServices } from "@effect/platform-bun";
 import { Layer } from "effect";
 import { Command, Flag } from "effect/unstable/cli";
 import type * as CliCommand from "effect/unstable/cli/Command";
@@ -20,11 +19,11 @@ const config = {
 export type LegacyEncryptionUpdateRootKeyFlags = CliCommand.Command.Config.Infer<typeof config>;
 
 // `Stdin` is new production wiring for this command. Provide it explicitly
-// (along with its `Tty` + `Stdio` deps) so the command's layer is self-contained
-// and does not rely on sibling-layer leakage inside `Layer.mergeAll`.
+// (along with its `Tty` dep) so the command's layer is self-contained and does
+// not rely on sibling-layer leakage inside `Layer.mergeAll`.
 const updateRuntime = Layer.mergeAll(
   legacyManagementApiRuntimeLayer(["encryption", "update-root-key"]),
-  stdinLayer.pipe(Layer.provide(ttyLayer), Layer.provide(BunServices.layer)),
+  stdinLayer.pipe(Layer.provide(ttyLayer)),
 );
 
 export const legacyEncryptionUpdateRootKeyCommand = Command.make("update-root-key", config).pipe(

apps/cli/src/legacy/commands/logout/logout.layers.ts

@@ -18,7 +18,7 @@ import { stdinLayer } from "../../../shared/runtime/stdin.layer.ts";
  * legacy CLAUDE.md item 5). `Analytics`, `Output`, `Stdio`, `Tty`, `FileSystem`,
  * `Path`, `TelemetryRuntime`, and `LegacyYesFlag` come from the root layer;
  * `stdinLayer` (the shared piped-stdin reader for the logout confirm) builds its
- * `Stdin` from the root `Stdio`/`Tty`, like the migration runtimes.
+ * `Stdin` from the root `Tty`, like the migration runtimes.
  */
 const cliSettings = legacyCliSettingsLayer.pipe(Layer.provide(legacyDebugLoggerLayer));
 const credentials = legacyCredentialsLayer.pipe(