Add Knowledge Graph stage and category to Analytics section

Summary

This MR adds the Knowledge Graph stage to the Analytics section of the product categories hierarchy, and adds the Knowledge Graph team to the relevant team member files.

Changes

• data/stages.yml: Adds a new knowledge_graph stage under the analytics section, with a single group (knowledge_graph) owned by PM Meg Corren and EM Michael Angelo Rivera. The group uses the Analytics:Knowledge Graph Team tag and lists Analytics Section (DRI: Nitin Singhal), AI Framework, Duo Chat, and Agent Foundations as internal customers.

• data/categories.yml: Adds a new knowledge_graph category with a planned maturity, available date of 2026-05-01, and a description derived from the GitLab Knowledge Graph architecture design document.

• data/team_members/person/*/: Adds team_tags: [Analytics:Knowledge Graph Team] to the four Knowledge Graph engineers — Michael Angelo Rivera, Bohdan Parkhomchuk, Michael Usachenko, and Jean-Gabriel Doyon — so they are automatically resolved on the categories page.

Context

The GitLab Knowledge Graph (Orbit) is a Rust service that builds a property graph from GitLab instance data — SDLC metadata and code structure — and exposes it through a unified context API for AI systems (via MCP) and human users. This MR formalizes Knowledge Graph as a stage under the Analytics section as the team grows.

/cc @megcorren @michaelangeloio