Expose plugin manifest keywords in app server

[alfozan]

Summary

• Add plugin manifest keywords to core plugin marketplace/detail models
• Expose keywords on app-server v2 PluginSummary and generated schema/types
• Populate keywords in plugin/list and plugin/read responses for local plugins

Depends on https://github.com/openai/openai/pull/891087

Validation

• just fmt
• just write-app-server-schema
• cargo test -p codex-app-server-protocol
• cargo test -p codex-core-plugins
• cargo test -p codex-app-server plugin_list_keeps_valid_marketplaces_when_another_marketplace_fails_to_load
• cargo test -p codex-app-server plugin_read_returns_plugin_details_with_bundle_contents

[github-actions]

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