feat: builder-style InputSpec API, prefill plumbing, and port forward fix

- Add addKey() and add() builder methods to InputSpec with InputSpecTools
- Move OuterType to last generic param on Value, List, and all dynamic methods
- Plumb prefill through getActionInput end-to-end (core → container-runtime → SDK)
- Filter port_forwards to enabled addresses only
- Bump SDK to 0.4.0-beta.50

sdk/base/lib/osBindings/GetActionInputParams.ts

@@ -2,4 +2,8 @@
 import type { ActionId } from './ActionId'
 import type { PackageId } from './PackageId'
 
-export type GetActionInputParams = { packageId?: PackageId; actionId: ActionId }
+export type GetActionInputParams = {
+  packageId?: PackageId
+  actionId: ActionId
+  prefill: Record<string, unknown> | null
+}