feat: milestone 5b — frontend bundle host + VerstakPluginAPI stub
- Bundle contract: window.VerstakPluginRegister(id, {components: {...}})
- PluginBundleHost.svelte: loads bundle via GetPluginAssetContent, mounts components
- VerstakPluginAPI.js: restricted API (capabilities, events, settings, commands — all stub)
- ViewContainer: PluginBundleHost replaces placeholder when frontend bundle exists
- PluginManager: settings panel via PluginBundleHost (removed hardcoded form)
- Backend: GetPluginFrontendInfo, GetPluginAssetContent with path security
- Security: reject absolute paths, path traversal, escape from plugin root
- Error boundary: bundle load/execute/mount errors show fallback, not crash
- Tests: 11 backend tests (asset API), frontend bundle checks in smoke
- Docs: bundle contract, VerstakPluginAPI, security constraints
mirivlad
05ef1449bc