Extract agent-kit + personal-stack adopt

[jorisjonkers-dev-agents]

Objective: pinned renderer/installer kit (Claude+Codex parity). Already a product installed into multiple repos.

Notes: preserve render-agent-kit.py --check/--write/--output/--doctor; include knowledge-api installer-serving model (InstallerController ClassPathResource, @Version@/@KB_URL@ substitution, platform/tooling tests for manifest + /install.sh Flux routes).

Work:

• Build ExtraToast/agent-kit from platform/agents/kit + council
• personal-stack consumes pinned kit; CI fails on drift of .claude/.codex/.agents/installer resource/runner entrypoint

Part of #605.