Add langgraph to AI and Agents (Orchestration)

[Oliver-Liu99]

Adds langgraph under AI and Agents → Orchestration.

Why it qualifies (all quality requirements met):

• Python-first: 99.6% Python
• Active: commits within the last days
• Stable: production-ready, 0.x releases used widely in production agent stacks
• Documented: thorough docs with quickstarts and examples
• Established: 34k+ stars

Acceptance criteria — Industry Standard for its niche:
The de-facto framework for graph-based, stateful agent orchestration (durable execution, human-in-the-loop, persistent memory), with very broad adoption.

Uniqueness (not a duplicate of langchain):
langchain is a composability layer for chaining LLM calls and integrations. langgraph is a separate, lower-level library that models an agent as a stateful graph with explicit nodes/edges, checkpointing/durable execution, and human-in-the-loop interrupts — used to build long-running agents that langchain itself does not provide. It is published as its own PyPI package (pip install langgraph).