fix(cli): update graph config schema to support description field (#6895)

## Summary
- The config processing code in `config.py` already handles graphs
defined as `{"path": "...", "description": "..."}` dicts, but the
`Config` TypedDict and JSON schema only declared `dict[str, str]`
- Added a `GraphDef` TypedDict with `path` and optional `description`
fields
- Updated `Config.graphs` to `dict[str, str | GraphDef]` and regenerated
the JSON schemas
- This makes the schema match the actual runtime behavior and fixes
IDE/schema validation for users who use the dict format

## Test plan
- [x] `make format` passes
- [x] `make lint` passes
- [x] `make test` passes (all 85 tests)
- [x] Schema regeneration produces consistent output

Release Notes: Update `langgraph.json` schema to support `{"path":
"...", "description": "..."}` format for graph definitions.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

libs/cli/generate_schema.py

@@ -20,6 +20,7 @@ from langgraph_cli.schemas import (
     Config,
     ConfigurableHeaderConfig,
     CorsConfig,
+    GraphDef,
     HttpConfig,
     IndexConfig,
     SecurityConfig,
@@ -108,6 +109,7 @@ def add_descriptions_to_schema(schema, cls):
             # Find the class that corresponds to this definition
             for potential_cls in [
                 Config,
+                GraphDef,
                 StoreConfig,
                 IndexConfig,
                 AuthConfig,