fix(config): optimize dependency installation to use global cache (#11147)

[xiaobluesky]

Fixes #11147
fix(config): optimize dependency installation to use global cache

Problem:

• OpenCode was creating node_modules in every .opencode directory
• Each installation duplicated @opencode-ai/plugin (~6MB each)
• Wasted disk space when working across multiple projects

Solution:

• Install @opencode-ai/plugin to ~/.cache/opencode/node_modules/ (shared global cache)
• Only create local node_modules when package.json has custom dependencies
• Skip dependency installation entirely if package.json does not exist

Result:

• Reduces disk usage by sharing @opencode-ai/plugin across all projects
• Maintains ability for users to add custom dependencies locally
• No longer creates redundant node_modules directories

[github-actions]

Thanks for your contribution!

This PR doesn't have a linked issue. All PRs must reference an existing issue.

Please:

1. Open an issue describing the bug/feature (if one doesn't exist)
2. Add Fixes #<number> or Closes #<number> to this PR description

See CONTRIBUTING.md for details.

[github-actions]

The following comment was made by an LLM, it may be inaccurate:

Based on the search results, I found two potentially related PRs:

1. feat(bun): track provider packages for automatic cleanup (feat(bun): track provider packages for automatic cleanup #10275)

   • feat(bun): track provider packages for automatic cleanup #10275
   • Related because it deals with package management and cleanup, which could intersect with the global cache approach

2. fix(core): plugins are always reinstalled (fix(core): plugins are always reinstalled  #9675)

   • fix(core): plugins are always reinstalled  #9675
   • Related because it addresses plugin reinstallation issues, which could be related to the dependency caching optimization

The primary PR (#11506) appears to be the current PR you're working with. The two related PRs above might have relevance to the dependency installation and caching improvements being made.