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/package/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "@start9labs/start-sdk",
-  "version": "0.4.0-beta.49",
+  "version": "0.4.0-beta.50",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "@start9labs/start-sdk",
-      "version": "0.4.0-beta.49",
+      "version": "0.4.0-beta.50",
       "license": "MIT",
       "dependencies": {
         "@iarna/toml": "^3.0.0",