Group the day-two docs and move How it's built to an About page #104

The day-two jobs (ship, observe, upgrade) are scattered, and How it's built reads like something a generated solution gets when it's really how we build the template.

Phase 1: Sidebar and framing

• Add an "Operate" group per template for ship the container, observe in production and upgrade
• Move How it's built to one shared About page for all five templates
• Pick one spelling: the site says "analyzers", AGENTS.md says "analysers"

Checks: the site builds and the link checker passes.