fix(showcase): fix showcase-harness build — commander dep + cli runner type alignment

Add missing `commander` dependency to showcase-harness package.json
(imported in cli.ts but never declared). Add index signatures to
SmokeInput and ChatToolsInput interfaces in targets.ts so they satisfy
the `{ [k: string]: unknown }` constraint from the Zod `.passthrough()`
schemas used by the liveness and e2e-chat-tools drivers.

Author: jpr5