Initial StartOS package for Station Master (v0.5.1)

Built from source via a git submodule pinned to a tag, not a published image
— the Dockerfile, main.ts, and manifest should never need to change for an
ordinary version bump, only the submodule pin (see UPDATING.md). One volume,
one interface serving the browser client + lobby/intent API + SSE stream
from a single origin, no dependencies. The server-wide join secret (D14) is
seeded on install, exposed via the Get Join Secret action, and blocks start
behind a critical task until retrieved — the same first-set/rotation pattern
as actual-budget-startos's admin password.

Verified on phoenix.local: installs, the critical task correctly blocks an
ordinary start, force-starting confirms the daemon binds its port and serves
the client, and store.json correctly holds the install-seeded join secret.
Not verified: the Get Join Secret action's execution end-to-end — start-cli's
`package action run` fails with a client-side deserialization error that
reproduces identically against actual-budget's already-shipped equivalent
action, so this looks like a start-cli issue rather than a defect here.

icon.svg is still the scaffold's hello-world placeholder — no real Station
Master icon exists yet to ship in its place.

startos/interfaces.ts

@@ -0,0 +1,28 @@
+import { i18n } from './i18n'
+import { sdk } from './sdk'
+import { uiPort } from './utils'
+
+// One interface: the server serves the browser client, the lobby/intent HTTP API, and the SSE
+// game stream all from this single port (deployment.md's same-origin rule in the game repo —
+// baking in a second origin would break relative URLs). type: 'ui' is a label the client is
+// meant for a browser; it does not stop the same port from also carrying the API calls that
+// client makes back to itself.
+export const setInterfaces = sdk.setupInterfaces(async ({ effects }) => {
+  const uiMulti = sdk.MultiHost.of(effects, 'ui-multi')
+  const uiMultiOrigin = await uiMulti.bindPort(uiPort, { protocol: 'http' })
+  const ui = sdk.createInterface(effects, {
+    name: i18n('Multiplayer Table'),
+    id: 'ui',
+    description: i18n('Create or join a game, and play in the browser'),
+    type: 'ui',
+    masked: false,
+    schemeOverride: null,
+    username: null,
+    path: '',
+    query: {},
+  })
+
+  const uiReceipt = await uiMultiOrigin.export([ui])
+
+  return [uiReceipt]
+})