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/tsconfig.json

@@ -23,6 +23,9 @@
     {
       "path": "../../host/apiproxy"
     },
+    {
+      "path": "../../session-projection/session-projection"
+    },
     {
       "path": "../../llm/llm"
     },