Add agentic AI addons

**Parent:** #584
**Priority:** Medium

Add addon registry entries and charts for agentic AI workloads:
- Amazon Bedrock Agent runtime integration
- LangChain/LangGraph operator
- Vector database (pgvector, Milvus, or Weaviate)
- Model serving infrastructure (vLLM, TGI)
- Agent orchestration (CrewAI, AutoGen)
- Evaluation and observability (LangSmith, Phoenix)

Define as a new registry file `ai.yaml` or extend `ml.yaml`.

Start by inspecting the existing addon registry files and charts to compare their structure with the proposed `ai.yaml` or `ml.yaml` location. Determine how the listed Bedrock, LangChain/LangGraph, vector database, model serving, orchestration, and evaluation integrations should be represented, and consider the registry-file choice part of the design before adding the complete set.

Written by the indexing model from the issue text.