fix(mode): run_code passes both layers as a transport — Code Mode composes with plan mode

Review finding, valid: under the registry's Code Mode the assembly's
only wire tool is run_code, which the plan allowlist filtered out —
leaving the model with NO tools at all, the exit review included. The
composition exists today (the acp-agent example ships a code-mode
overlay), so plan mode bricked it outright.

run_code is a transport, not a capability: every bridged sub-call is
serialized back through ToolRegistry.execute() carrying the same agent,
so tools/pre-execute judges each capability individually — exactly like
native calls. Both layers now exempt it by name: the filter keeps it
visible (tests pin plan-mode Code Mode assembly = ['run_code']) and the
gate passes the wrapper while the same run's write sub-call still
denies with the plan-mode reason.

Documented residual, same class as the prepend-after-load one: the SDK
section renders from the registry's store, so a plan-mode program may
be offered bindings whose dispatch the gate then denies — nothing runs
that a native call could not.

packages/mode/mode/package.json

@@ -32,6 +32,7 @@
   "devDependencies": {
     "@deepseek-ai/dsh-agent": "workspace:^",
     "@deepseek-ai/dsh-agent-loop": "workspace:^",
+    "@deepseek-ai/dsh-code-runtime": "workspace:^",
     "@deepseek-ai/dsh-llm": "workspace:^",
     "@deepseek-ai/dsh-session": "workspace:^",
     "@deepseek-ai/dsh-system-prompt": "workspace:^",