fix: wait for dependencies before loading custom tools and plugins

[thdxr]

Summary

Fixes a race condition where custom tools with external dependencies in their package.json would crash on import because dependencies weren't installed yet.

Problem

When a custom tool file had an import like:

import { say } from 'cowsay'

at the top level, and the tool directory had a package.json with cowsay as a dependency, the tool would crash with "Cannot find package 'cowsay'" because dependencies weren't installed before the module was imported.

Solution

1. Config.state() now collects dependency installation promises in a deps array using iife()
2. Added Config.waitForDependencies() to await all installations before proceeding
3. ToolRegistry calls waitForDependencies() before loading custom tools (if tools exist)
4. Plugin.list() calls waitForDependencies() before loading plugins (if plugins exist)

Changes

• packages/opencode/src/config/config.ts: Track deps array and add wait function
• packages/opencode/src/tool/registry.ts: Wait for deps before loading tools
• packages/opencode/src/plugin/index.ts: Wait for deps before loading plugins
• packages/opencode/test/tool/registry.test.ts: Added test verifying tools with external deps (cowsay) load successfully

Testing

Added a test that creates a tool with cowsay as a dependency and imports it at the top level. The test verifies the tool loads without crashing.