fix(deals): drop runtime @opencode-ai/plugin import so the plugin loads

The cmd_plan_summary tool imported `tool` from `@opencode-ai/plugin` at
runtime. That package is an optional peer dependency: `opencode plugin <pkg>`
installs it in `.opencode/`, not next to the plugin, so the import threw
ERR_MODULE_NOT_FOUND at load and killed the whole server plugin — no
auto-registration and no /connect entry (Command Code vanished from the
provider list).

Build the tool's Zod args from a direct `zod` dependency instead, and add a
contract test that scans dist/ for runtime `@opencode-ai/*` imports.