#24 Repo name via flags/env (header + title + feed)

Context: Owner round — like description (#21), the repo display name must be settable via config (flags/env, no config file), with a sensible fallback. Tasks:

1. --repo-name S + HU13_REPO_NAME (flag > env > fallback: directory name of repo). Thread into header brand area, <title>, og:title, feed title, api consumers (add to meta where trivial, keep api shapes stable otherwise).
2. Escaping: hostile name renders as text. Empty string = fall back (never blank header).
3. Entrypoint passes HU13_REPO_NAME. Demo: supervisor sets it on hu13-live alongside HU13_DESCRIPTION.
4. Tests: chain (flag beats env beats dirname), escaping, empty-fallback. Success rubric:

• Name correct in header/title/og/feed; chain + escaping tested. Swarm: fold into the #21 agent (same header code) — branch m6/header-config, close both.