feat(opencode): add plugin management CLI commands

[sgwannabe]

Summary

Add CLI commands for managing OpenCode plugins, addressing the need for easy plugin updates without manual config editing.

Fixes #6159

Changes

Add opencode plugin subcommand with:

• list - List installed plugins with current/latest version comparison
• update [name] - Update all or specific plugin to latest version
• add <name> - Add a plugin to config
• remove <name> - Remove a plugin from config

Implementation Details

• Uses existing utilities: Config.getPluginName() for consistent name extraction, BunProc.install() for package installation
• Scoped package support: URL-encodes package names for npm registry fetches (@scope/pkg → %40scope%2Fpkg)
• Input normalization: update [email protected] and remove [email protected] correctly match foo plugin
• Config validation: Safely handles non-array plugin field
• Atomic config writes: Uses temp file + rename pattern to prevent corruption
• Proper error handling: Distinguishes ENOENT (create new) from JSON parse errors (throw)
• Truthful status reporting: Shows "latest unknown" when registry fetch fails instead of "up to date"
• Spinner lifecycle: Properly stops spinner before re-starting

Demo Output

$ opencode plugin list
┌  Installed Plugins
◇  Version check complete
│
●  ✓ oh-my-opencode 2.14.0
●  ⬆ opencode-anthropic-auth 0.0.7 → 0.0.8
●  ! @scope/plugin 1.0.0 (latest unknown)
│
└  3 plugin(s), 1 update(s) available, 1 check(s) failed. Run: opencode plugin update

$ opencode plugin update
┌  Update Plugins
●    opencode-anthropic-auth 0.0.7 → 0.0.8
◇  ✓ opencode-anthropic-auth updated to 0.0.8
│
└  1 plugin(s) updated

How to verify

# List plugins and their versions
opencode plugin list

# Add a new plugin
opencode plugin add example-plugin

# Update all plugins
opencode plugin update

# Update specific plugin (accepts name with or without version)
opencode plugin update oh-my-opencode
opencode plugin update [email protected]  # also works

# Remove a plugin (accepts name with or without version)
opencode plugin remove example-plugin
opencode plugin remove [email protected]  # also works

Testing Done

• plugin list - shows installed plugins with version info
• plugin list - shows "latest unknown" when fetch fails
• plugin update - updates all plugins to latest
• plugin update <name> - updates specific plugin
• plugin update <name>@<version> - normalizes input correctly
• plugin add <name> - installs and adds plugin to config
• plugin add <name>@<version> - installs specific version
• plugin remove <name> - removes plugin from config
• plugin remove <name>@<version> - normalizes input correctly
• Error case: plugin not found (shows available plugins)
• Error case: npm fetch failure (reports as skipped)
• Local file:// plugins are skipped appropriately
• Typecheck passes

[github-actions]

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

No duplicate PRs found