refactor(gui): source SessionProjectionMap from the interface package's pure-type outlet

Swap the client runtime's parallel-construction placeholder for
import type from @deepseek-ai/dsh-session-projection/types — the zero-import
outlet, never the package root, whose dsh-agent → dsh-session chain would drag
the host Context.sessions merge into the client program. One type table end to
end (host provider, wire block, client cell, React hook); the spec's test key
now declare-merges the real module. Adds the workspace dep and the tsconfig
project reference.

packages/client/runtime/package.json

@@ -36,6 +36,7 @@
     "@deepseek-ai/dsh-host-apiproxy": "workspace:^",
     "@deepseek-ai/dsh-llm": "workspace:^",
     "@deepseek-ai/dsh-session": "workspace:^",
+    "@deepseek-ai/dsh-session-projection": "workspace:^",
     "immer": "^10.1.1",
     "react": "^18.2.0",
     "zustand": "~4.4.7"