security: Sandbox WAM dynamic imports and custom plugin GUIs

[ChuxiJ]

Problem

Custom HTTPS WAM URLs are dynamically imported into the app context, and plugin GUIs are appended directly into the DOM. Protocol validation blocks obvious javascript:/data: URLs, but there is no allowlist, integrity check, permission boundary, or iframe/sandbox isolation.

Root Cause

WAM support prioritized functionality first and did not complete a browser security boundary for remote plugin code and GUI surfaces.

Solution

• Define allowed WAM source policy for built-in, trusted remote, and custom URLs.
• Add allowlist and optional integrity/hash metadata for remote modules.
• Sandbox plugin GUI rendering where feasible.
• Add warning/confirmation UX for untrusted custom plugin URLs.
• Document the trust model.

Verification

• Add tests for blocked protocols, untrusted origins, and allowlisted URLs.
• Add E2E/manual QA for custom URL warning and GUI isolation.
• Review CSP and Tauri/webview implications.

Files to Touch

• src/services/wam/WAMHost.ts
• src/components/plugins/WAMPluginBrowser.tsx
• src/components/plugins/WAMPluginPanel.tsx
• src/types/wam.ts
• docs/security/*