Add remote plugin uninstall API

[xli-oai]

Summary

• Adds the remote plugin/uninstall request form using required pluginId plus optional remoteMarketplaceName, while preserving local pluginId uninstall.
• Adds codex_core_plugins::remote::uninstall_remote_plugin for the deployed ChatGPT plugin backend uninstall path and validates the backend returns the same id with enabled: false.
• Routes app-server remote uninstall through feature checks, remote plugin id validation, backend mutation, local downloaded cache deletion, cache clearing, docs, and regenerated protocol schemas.

Tests

• just write-app-server-schema
• just fmt
• cargo test -p codex-app-server-protocol plugin_uninstall_params_serialization_omits_force_remote_sync
• cargo test -p codex-app-server plugin_uninstall --test all
• cargo test -p codex-app-server plugin_uninstall
• cargo build -p codex-cli
• CODEX_BIN=/Users/xli/code/codex/codex-rs/target/debug/codex python3 /Users/xli/.codex/skills/xli-test-marketplace-api/scripts/run_marketplace_api_matrix.py (44 pass / 0 fail)
• just fix -p codex-app-server-protocol -p codex-app-server -p codex-tui
• just fix -p codex-app-server

[chatgpt-codex-connector]

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[xli-oai]

@codex review

[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 689b3d11db

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