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.

instructions.md

@@ -0,0 +1,38 @@
+# Station Master
+
+## Documentation
+
+- [Rules and design docs](https://draco.local:53871/Jesse.Markowitz/station-master/src/branch/main/docs)
+  — the rulebook implications, the multiplayer design, and the game's architecture.
+
+## What you get on StartOS
+
+This service runs the multiplayer server: a lobby, and a table for 2 to 4 players to play a
+competitive or cooperative game together from their own browsers. Everything a player needs — the
+game itself, the lobby, and the connection back to this server — is served from the single web
+interface below; there is nothing else to install or configure on a player's side.
+
+## Getting set up
+
+1. Open this service's **Multiplayer Table** interface.
+2. Run the **Get Join Secret** action from this service's Actions menu, and copy the value it
+   returns.
+3. Share that secret, and the address you opened the interface at, with everyone you want to
+   play with. Anyone holding the secret can create a new game or join one that hasn't started yet.
+4. In the browser, click **Multiplayer**, then **Create Game** (or **Join Game** with a game code
+   someone else created), and enter the join secret when asked.
+
+## Using Station Master
+
+### Multiplayer Table
+
+Create or join a game, seat players (including filling empty seats with a bot), and start. Once a
+game is underway, this same interface is where every player plays their turns and watches the
+table — there is nothing else to open.
+
+### Get Join Secret
+
+Run this whenever you need the current join secret again, or want to shut out anyone still
+holding an old one. Every run replaces the secret and immediately puts the new one into effect —
+players already seated in a game are unaffected, but the old secret stops working for creating or
+joining games from that point on.