Slice 1: surface system + WS transport + composition root

Pure-core feature libraries assembled at the composition root:
- core/protocol: pure reducer over surface catalog/spec/error messages
- features/surface-host: generic field-kind interpreter (toggle/progress/
  selector/stat/button) + pure plan logic; no surface-id special-casing
- adapters/ws: injected WebSocket client (effects at the edge)
- app: composition root store (Svelte 5 runes over the pure reducer),
  host-relative surface WS URL resolution (resolveWsUrl), root App.svelte

Verified green: svelte-check 0/0, vitest 84 passed, biome clean, vite build ok.

1 files changed, 3 insertions, 0 deletions

diff --git a/src/features/surface-host/index.ts b/src/features/surface-host/index.ts
new file mode 100644
index 0000000..afa3127
--- /dev/null
+++ b/src/features/surface-host/index.ts
@@ -0,0 +1,3 @@
+export { buildInvoke, planSurface } from "./logic/plan";
+export type { FieldView, SurfaceRenderPlan } from "./logic/types";
+export { default as SurfaceView } from "./ui/SurfaceView.svelte";