Transmission #021: README, SSH setup, and remote reload cwd

Added a root README.md so new contributors have a single place for clone layout, local dev pointers, SSH key setup for ./scripts/helerion-remote-reload.sh, env overrides (HELERION_SSH_*, HELERION_REMOTE_RELOAD), and troubleshooting. AGENTS.md now has a Repository setup section so agents point “how do I set up the repo?” questions at that README; the helerion-publish skill links the SSH section under prerequisites.

The default command for scripts/helerion-remote-reload.sh is cd ~/infra && ./reload-helerion.sh (not cd ~ && ./infra/...). The home reload-helerion.sh uses relative paths (e.g. cd helerion/); the working directory must be ~/infra so those resolve. HELERION_REMOTE_RELOAD still overrides when a host layout differs.

Reload over SSH was verified end-to-end after the cwd fix.