Episode 10: hardening - firewall rules Docker cannot bypass, Caddy access log and rate limiting, fail2ban in the right chain

- hardening/: ufw after.rules block for DOCKER-USER (ctorigdstport, not dport),
  fail2ban jail.local with sshd (systemd backend) and caddy-probes (chain DOCKER-USER),
  filter for the JSON access log, sshd hardening.conf, README with the order and
  the two traps measured in the episode
- caddy/Dockerfile: xcaddy build with caddy-ratelimit, compose builds the image
- Caddyfile: common snippet (JSON access log, Server header stripped), vault /admin 404,
  rate_limit zones on the vault token endpoint and the git login form
- HARDENING.md: firewall and fail2ban sections rewritten around what the port scan saw

Claude-Session: https://claude.ai/code/session_017iP581CYtPfxdZYPPAyWZA

caddy/Dockerfile

@@ -0,0 +1,9 @@
+# episode 10: the stock caddy:2-alpine image cannot rate limit. The directive
+# lives in a plugin (github.com/mholt/caddy-ratelimit) that has to be compiled
+# in with xcaddy - there is no runtime "enable" for it. Two stages so the final
+# image stays the same small alpine, just with our own caddy binary.
+FROM caddy:2-builder-alpine AS builder
+RUN xcaddy build --with github.com/mholt/caddy-ratelimit
+
+FROM caddy:2-alpine
+COPY --from=builder /usr/bin/caddy /usr/bin/caddy