Allow plugin installations to be cancelled

[debba]

Summary

• turn the install action into a cancel button while a plugin is downloading
• stop the active request and extraction, then remove staged files
• keep an existing plugin active until its replacement is verified and ready
• improve the registry card layout and installation states

Testing

• pnpm exec eslint src/components/settings/PluginsTab.tsx
• pnpm typecheck
• cargo check --manifest-path src-tauri/Cargo.toml
• cargo test --manifest-path src-tauri/Cargo.toml plugins::tests::

[kilo-code-bot]

Code Review Summary

Status: No Issues Found | Recommendation: Merge

Files Reviewed (7 files)

• src-tauri/src/lib.rs
• src-tauri/src/plugins/commands.rs
• src-tauri/src/plugins/install_cancellation.rs
• src-tauri/src/plugins/installer.rs
• src-tauri/src/plugins/mod.rs
• src-tauri/src/plugins/tests.rs
• src/components/settings/PluginsTab.tsx

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_{Reviewed by glm-5.2 · Input: 37.6K · Output: 9.8K · Cached: 106.9K}