…rvices

Replace the tmpdir + short-lived spawn machinery in withCliFixture:

- `os.tmpdir + fs.mkdir + addFinalizer` → `FileSystem.makeTempDirectoryScoped`.
  Cleanup is now scope-driven without a hand-rolled finalizer.

- `Process.run` (legacy cross-spawn wrapper) → `AppProcess.run`, which is the
  same service already used by `git`, `ripgrep`, `format`, `mcp`, etc.
  One spawn primitive across src + tests.

`stdin: "ignore"` is set explicitly because `ChildProcess.make` defaults
stdin to "pipe", which caused `opencode run` to block on `Bun.stdin.text()`
waiting for an EOF that the test never sent. The old wrapper defaulted to
ignore, so this preserves the prior contract.

`AppFileSystem.defaultLayer` + `AppProcess.defaultLayer` are provided
internally so callers' signatures don't change.

The help-snapshot path regex widens from `[a-z0-9]+` to `[A-Za-z0-9]+`
because Node's `mkdtemp` suffix is mixed-case (unlike the prior
`Math.random().toString(36)` suffix).

Slice 1 of 2. Slice 2 will migrate the long-lived `serve` / `acp`
builders, which use raw `Bun.spawn` today.

Two simplify-pass refinements on top of the harness migration:

1. Pass `timeout` into `AppProcess.run` instead of wrapping with an
   external `Effect.timeoutOrElse`. AppProcess.run is itself scoped, so
   the built-in timeout triggers the acquireRelease kill finalizer
   *before* surfacing the error — guaranteeing the child is dead by the
   time the test continues. The external wrapper variant raced the
   scope close and could leak the child past the test boundary.

2. Replace `Effect.orDie` with `Effect.catchTag("AppProcessError", ...)`
   so timeouts AND spawn failures both turn into a synthetic non-zero
   result with the error's command / stderr / cause as diagnostics —
   instead of crashing as a defect. The synthetic result is `satisfies
   AppProcess.RunResult` so it stays in sync with process.ts.

3. Name the spawn Effect span `"opencode.spawn"` via `Effect.fn` to
   match the existing `Effect.fn("opencode.serve")` / `.acp` siblings.