Fix plugin loading: move @opencode-ai/plugin to dependencies

[hakanai3d]

Summary

This PR fixes a plugin loading issue when installed via npm by moving @opencode-ai/plugin from devDependencies to dependencies.

The Problem

When the plugin is installed from npm, devDependencies are not included. This caused the plugin to fail with:
ERROR: Cannot find module '@opencode-ai/plugin'

Root Cause

The plugin expects @opencode-ai/plugin to be available at runtime (as a peer dependency provided by opencode). However, opencode's module resolution for npm plugins doesn't properly resolve peer dependencies from the global config directory.

This Fix

Moving @opencode-ai/plugin to dependencies ensures it's bundled with the plugin package, making module resolution work reliably.

• EDIT:
  -- Version pinned to ~1.3.13 to prevent breaking changes while allowing patch updates
  -- @opencode-ai/plugin kept in peerDependencies for documentation purposes

Trade-offs:

• Works immediately and reliably
• No changes needed to opencode core

• Duplicates @opencode-ai/plugin across plugin installations
• Not architecturally ideal (peer dependency would be cleaner)

Alternative Approaches

A more elegant solution might be for opencode to:

1. Provide @opencode-ai/plugin as a global peer dependency
2. Set up module resolution to find it from ~/.config/opencode/node_modules/
   However, that requires changes to opencode core. This PR is a pragmatic fix that works with the current architecture.

Testing

After this fix, the plugin loads successfully and all tools are registered:

• codebase_search - Search code by meaning
• codebase_peek - Find code locations by meaning
• index_codebase - Index codebase for search
• index_status - Check index status
• index_health_check - Check index health
• index_metrics - Get index metrics
• index_logs - Get indexer logs
• find_similar - Find similar code
• call_graph - Query function callers/callees
• implementation_lookup - Find symbol definitions

[Helweg]

If this is really needed because OpenCode doesn’t resolve peer deps reliably for npm plugins, I’m okay with it. I’d just prefer we pin @opencode-ai/plugin more tightly (exact or ~ rather than ^) and leave a quick note about why we’re doing this.

[Helweg]

The tighter pin looks good, but I think there’s one follow-up issue here: package.json can’t contain // comments, so the inline notes make the manifest invalid JSON. I’d move that explanation to the PR description/README/changelog and then regenerate package-lock.json as well so it matches the new ~1.3.13 range.

[hakanai3d]

doh comments in JSON! fixed