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.

icon.svg

@@ -0,0 +1,11 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 512 512">
+  <defs>
+    <linearGradient id="bg" x1="0" y1="0" x2="1" y2="1">
+      <stop offset="0%" stop-color="#4F46E5"/>
+      <stop offset="100%" stop-color="#7C3AED"/>
+    </linearGradient>
+  </defs>
+  <rect width="512" height="512" rx="96" fill="url(#bg)"/>
+  <path d="M256 120c-88.4 0-160 58.1-160 129.8 0 41.4 23.6 78.4 60.5 103.2l-12.9 51.5a8 8 0 0 0 11.6 8.8l62.6-36.1c12.3 2.5 25.2 3.8 38.2 3.8 88.4 0 160-58.1 160-129.8S344.4 120 256 120z" fill="white" opacity="0.95"/>
+  <text x="256" y="270" text-anchor="middle" font-family="Arial, Helvetica, sans-serif" font-weight="bold" font-size="64" fill="#4F46E5">Hello!</text>
+</svg>