Extract the shared in-process driver into dsh-subagent-inprocess (review feedback)

The shared run driver lived inside dsh-subagent-spawn, so the spawn package
carried fork-aware seeding logic and dsh-subagent-fork depended backward on
dsh-subagent-spawn — the two in-process backends were not independent.

Move the driver (startInProcessRun, depthOf, SubagentDepthError,
InProcessRunOptions) into a new pure-library package
@deepseek-ai/dsh-subagent-inprocess that registers nothing. spawn and fork now
both depend only on that driver and neither knows about the other; spawn no
longer re-exports it and fork no longer imports from spawn.

Also wire BOTH backends in examples/coding-agent/cordis.yml (config-only): load
dsh-subagent-spawn + dsh-subagent-fork + two dsh-tool-subagent instances with
distinct toolNames (subagent → spawn, subagent_fork → fork), demonstrating that
exposing multiple transports needs no code change.

packages/subagent/subagent-spawn/tsconfig.json

@@ -17,17 +17,11 @@
     {
       "path": "../../../vendor/schemastery"
     },
-    {
-      "path": "../../core/agent"
-    },
-    {
-      "path": "../../llm/llm"
-    },
-    {
-      "path": "../../core/session"
-    },
     {
       "path": "../subagent"
+    },
+    {
+      "path": "../subagent-inprocess"
     }
   ]
 }