fix(plugin): export Promise ToolEditor

[kitlangton]

Why

Promise plugin authors cannot import ToolEditor to type reusable transform helpers: TypeScript reports that the module declares it locally but does not export it. The Effect API and the other public editor interfaces already export their editor types.

What Changes

Export the existing Promise interface without changing its members:

import type { ToolEditor } from "@opencode-ai/plugin/promise/tool"

function removeLegacyTool(editor: ToolEditor) {
  editor.remove("legacy")
}

Before: this named type import fails with TS2459. After: a separate source-linked consumer can import it and use the editor's methods.

Scope

One export keyword. No runtime changes, method renames, or changes to the Effect API.

Verification

# packages/plugin
bun typecheck
TMPDIR="$(realpath "${TMPDIR:-/tmp}")" bun run test

# separate source-linked consumer package
bun typecheck

# repository root
bunx prettier --check packages/plugin/src/promise/tool.ts
git diff --check

The consumer check failed with TS2459 before the change and passed afterward. Package typechecking, all 9 plugin tests, formatting, and the normal pre-push workspace typecheck pass. TMPDIR is canonicalized so the existing host-resolution tests compare the same filesystem path spelling on macOS.