cli: rename langgraph.json to langsmith.json

Rename the default config filename from `langgraph.json` to
`langsmith.json` as part of the "LangGraph Platform" to "LangSmith
Deployment" rebranding.

Backward compatibility is preserved: the CLI falls back to
`langgraph.json` with a deprecation warning when `langsmith.json`
is not found. A new `_resolve_config` callback handles the
resolution logic for all `--config` click options.

Changes span libs/cli (core logic, examples, tests), libs/sdk-py
(docstrings), libs/langgraph (Makefile), and .github CI scripts.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

libs/cli/langgraph_cli/util.py

@@ -21,7 +21,7 @@ def warn_non_wolfi_distro(config_json: dict) -> None:
             fg="yellow",
         )
         click.secho(
-            '   To switch, add \'"image_distro": "wolfi"\' to your langgraph.json config file.',
+            '   To switch, add \'"image_distro": "wolfi"\' to your langsmith.json config file.',
             fg="yellow",
         )
         click.secho("")  # Empty line for better readability