- Settings → System gains a 'default workspace storage path' item: validated
on save (absolute, creatable), applied immediately without restart, and
re-applied from the database on startup. Blank clears the override;
existing data is never migrated.
- Desktop local file/command tools get a renderer settings page (allowed
directory list with per-row delete, add via native picker, enable toggle,
tunnel status); the native dialog additionally gains a 'remove directory'
flow, fixing the whitelist that could only grow.
- System settings save surfaces backend validation errors as a toast.
Adds a read-only GET /api/v1/settings/search-providers catalog (admin-gated, no secrets), grouped collapsible provider cards, and a schema-driven plugin config form. Breaks a SystemSettingService<->PluginManager circular dependency via parameter @Lazy (with a context smoke test), and fixes PluginManager.updateConfig to merge instead of overwrite so omitted/blank secret fields are preserved. Hardens plugin search-provider id validation (reject-not-trim, case-insensitive conflict) and insulates the provider bridge hot path from throwing plugin code.
