Generic agents with per-host adapters stamped by install.sh

[sgraczyk]

Problem

agents/implement-minimal.md uses Claude-only keys. Skills use Claude-only sections. Generic hosts get Claude behavior.

Change

Keep one generic agent body with no host keys. Add tier light or heavy per agent. Add small per-host adapters. Add install.sh --host NAME and --model NAME. The installer stamps host fields on the installed copy. Record model values in supported-hosts.md. Keep Claude as one adapter.

Accept

• Generic files hold no host-only keys.
• Each agent declares a tier.
• install.sh --host and --model work for Claude, Codex, opencode, pi.
• Cheap models serve light tiers by default.