[FEATURE] Bulk install all plugins from a marketplace

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When using a marketplace (especially a team or personal marketplace), there's no way to install all plugins at once. Each plugin must be installed individually:

/plugin install law-tools@scl-marketplace
/plugin install writing@scl-marketplace
/plugin install dev-terminal@scl-marketplace
/plugin install docx-tools@scl-marketplace
/plugin install cc-toolkit@scl-marketplace
/plugin install pptx-tools@scl-marketplace

For marketplaces with many plugins, this is tedious and error-prone. New plugins added to the marketplace require manual discovery and installation.

Proposed Solution

Add a bulk install command:

/plugin install-all <marketplace>

Or use wildcard syntax consistent with other CLI patterns:

/plugin install *@scl-marketplace

Behavior:

• Installs all plugins defined in the marketplace's marketplace.json
• Skips plugins already installed (or updates them if newer version available)
• Reports summary: "Installed 4 plugins, 2 already up to date"

Alternative Solutions

1. Manual scripting - Parse marketplace.json and run individual install commands
2. Direct JSON editing - Manually add entries to ~/.claude/plugins/installed_plugins.json
3. Default-enabled flag (#17117) - Related but different; that feature auto-enables on individual install, this feature installs everything at once

Priority

Low - Quality of life improvement

Feature Category

CLI commands and flags

Use Case Example

1. Team onboarding - New developer joins, adds company marketplace, installs all standard tooling in one command
2. Personal tooling sync - User maintains a personal marketplace across machines, wants to replicate full setup quickly
3. Marketplace updates - When new plugins are added to a marketplace, easily install them without tracking what's new

Additional Context

Related issues:

• #14843 - Bulk enable/disable plugins (different: about toggling, not installing)
• #17117 - Default-enabled flag in marketplace.json (different: about auto-enable on individual install)
• #12840 - Headless/programmatic installation (complementary: would benefit from bulk install support)