Onboard - establish what this repo actually is

Use when a repo's own shape has not been established yet - the first better-dev session in a project, or a later one after the branch model, the stack, or the verify surface moved and the recorded facts went stale. It reads the repo and records what it found as standing facts in your harness's durable memory - the stack, the test and lint commands, the branch model and its integration branch, the team-or-solo shape, and whether guardrails exist - so later sessions and every other skill get those facts without re-deriving them. It writes no files into the repo. Also use to clean up a repo still carrying a managed better-dev block written by an earlier version, which comes …