fix(stdio-agent): declare the dsh-llm dependency the moved spec uses

stdio-chat.spec.ts imports ContentBlock/StreamChunk types from
@deepseek-ai/dsh-llm; the manifest entry lived on the folded package
and did not move with the tests. Declared peer+dev like the module's
other harness deps (the src consumes dsh-llm vocabulary through the
session events it renders).

pnpm-lock.yaml

@@ -897,6 +897,9 @@ importers:
       '@deepseek-ai/dsh-agent-core':
         specifier: workspace:^
         version: link:../../core/agent-core
+      '@deepseek-ai/dsh-llm':
+        specifier: workspace:^
+        version: link:../../llm/llm
       '@deepseek-ai/dsh-session':
         specifier: workspace:^
         version: link:../../core/session