docs(demo): clarify pinning in README and 02_langchain comment

- demo/README.md: reword note to say the embedded Colab install is
  commit-pinned; Colab links target main (not pinned)
- 02_langchain: update install cell comment to mention that both
  coordinode-embedded and langchain-coordinode are pinned (git commit);
  remaining pure-Python packages remain unpinned

Author: polaz

demo/README.md

@@ -13,7 +13,7 @@ Interactive notebooks for LlamaIndex, LangChain, and LangGraph integrations.
 
 > **Note:** First run installs `coordinode-embedded` from source (Rust build, ~5 min).
 > Subsequent runs use Colab's pip cache.
-> Notebooks are pinned to a specific commit that bundles coordinode-rs v0.3.15 (embedded engine used in Colab).
+> The embedded Colab install is pinned to a specific commit that bundles coordinode-rs v0.3.15; the Colab notebook links above target `main`.
 > The Docker Compose stack below uses the CoordiNode **server** image v0.3.15.
 
 ## Run locally (Docker Compose)

demo/notebooks/02_langchain_graph_chain.ipynb

@@ -86,8 +86,11 @@
     "        timeout=600,\n",
     "    )\n",
     "\n",
-    "# coordinode-embedded is pinned to a specific git commit because it requires a Rust\n",
-    "# build (maturin/pyo3) and the embedded engine must match the Python SDK version.\n",
+    "# coordinode-embedded and langchain-coordinode are pinned to a specific git commit:\n",
+    "# - coordinode-embedded requires a Rust build (maturin/pyo3); the embedded engine\n",
+    "#   must match the Python SDK version.\n",
+    "# - langchain-coordinode is pinned to the same commit so CoordinodeGraph(client=...)\n",
+    "#   is available; this parameter is not yet released to PyPI.\n",
     "# The remaining packages (coordinode, LangChain, etc.) are installed without pins:\n",
     "# they are pure Python, release frequently, and pip resolves a compatible version.\n",
     "subprocess.run(\n",