docs: add a getting-started guide and move README reference sections here Getting started is the five-step on-ramp the README now points at: host mode first, one recipe for a session, save a stack, then the container boundary. Build-and-images, supply-chain, and alternatives carry the sections the README used to hold, so the README can lead with what harnessed is for. recipe-catalog: replace the 2026-07-05 availability list with the shipped and planned list (the recipes.backlog directory is the authority), drop the agent-carnet, beads, and hyperpowers rows that no longer exist on main, and make the suggested stacks harness-free like every other stack. Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01XDyJrkAxgG1zkwhnZ4vkY1