Add StartOS 0.4 package scaffold (manifest, main, interfaces, 2 actions)

- package/Makefile + s9pk.mk + package.json + tsconfig.json
- startos/manifest: dockerBuild source pointing at ../image/Dockerfile
- startos/main: reads /data/config.yaml reactively, passes env vars to container
- startos/interfaces: binds port 9999 as HTTP UI
- startos/actions: showPublicKey (read /data/ssh/id_ed25519.pub), configureSparks
- TS + JS bundle compile clean (tsc --noEmit, ncc build)

package/startos/actions/configureSparks.ts

@@ -0,0 +1,60 @@
+import { sdk } from '../sdk'
+import { sparkConfigYaml } from '../fileModels/sparkConfig.yaml'
+
+const { InputSpec, Value } = sdk
+
+const inputSpec = InputSpec.of({
+  spark1_host: Value.text({
+    name: 'Spark 1 hostname or IP',
+    description: 'Head node. Example: <spark-1-ip>',
+    required: true,
+    default: null,
+    placeholder: '<spark-1-ip>',
+    masked: false,
+  }),
+  spark1_user: Value.text({
+    name: 'Spark 1 SSH user',
+    description: 'Usually "<spark-user>".',
+    required: true,
+    default: '<spark-user>',
+    placeholder: '<spark-user>',
+    masked: false,
+  }),
+  spark2_host: Value.text({
+    name: 'Spark 2 hostname or IP',
+    description: 'Worker node. Example: <spark-2-ip>',
+    required: true,
+    default: null,
+    placeholder: '<spark-2-ip>',
+    masked: false,
+  }),
+  spark2_user: Value.text({
+    name: 'Spark 2 SSH user',
+    description: 'Usually "<spark-user>".',
+    required: true,
+    default: '<spark-user>',
+    placeholder: '<spark-user>',
+    masked: false,
+  }),
+})
+
+export const configureSparks = sdk.Action.withInput(
+  'configure-sparks',
+  async () => ({
+    name: 'Configure Sparks',
+    description: 'Set the hostnames and SSH users for your two Spark nodes.',
+    warning: null,
+    visibility: 'enabled',
+    allowedStatuses: 'any',
+    group: null,
+  }),
+  async () => inputSpec,
+  async ({ effects }) => {
+    const cfg = await sparkConfigYaml.read().once()
+    return cfg ?? null
+  },
+  async ({ effects, input }) => {
+    await sparkConfigYaml.merge(effects, input)
+    return null
+  },
+)