scaffold: project skeleton, schema, healthz/readyz, CI

Initial project structure for neuronetz-gateway per scope-docs/SPEC.md:

- Python 3.12 / FastAPI / SQLAlchemy 2.0 (async) / Redis / Postgres stack
  managed by uv. Multi-stage non-root Dockerfile, prod + dev compose files
  (ollama service is NEVER published in either), Caddyfile + systemd unit,
  justfile, GitHub Actions CI (ruff, mypy --strict, pytest, bandit, pip-audit).
- Pydantic-Settings config covering every env var from SPEC §7, including the
  MODEL_DISCOVERY_* keys for the dynamic-discovery feature (§4.6).
- Alembic 0001_initial creates the full gateway schema (8 tables, 3 enums,
  notify_key_revoked() trigger), incl. allow_all_models on tenant_limits and
  key_limits for the per-tenant auto-grant toggle.
- Working /healthz, /readyz (fail-closed when deps unreachable), and a
  Prometheus /metrics stub. Sanitizing error handlers that attach X-Request-ID
  to every response and never leak upstream internals.
- SPEC + AGENT_PROMPT included under scope-docs/ (source of truth).

ops/caddy/Caddyfile.example

@@ -0,0 +1,59 @@
+# neuronetz-gateway — Caddy reverse proxy (SPEC §4.1, §6.5).
+#
+# Caddy is the only public-facing component. It terminates TLS (HTTP/2 + HTTP/3),
+# obtains a Let's Encrypt certificate for api.neuronetz.ai automatically, applies
+# security headers, and reverse-proxies to the internal-only gateway:8080.
+#
+# Copy this file to `Caddyfile` and edit the site address / admin email.
+# The production docker-compose.yml mounts it at /etc/caddy/Caddyfile.
+{
+	# Email for Let's Encrypt account + expiry notices. Replace before deploy.
+	email ops@neuronetz.ai
+}
+
+api.neuronetz.ai {
+	# --- Reverse proxy to the internal gateway ---
+	# `gateway` is the Docker service name on the internal network; it is never
+	# published to the host. Caddy forwards plain HTTP/1.1 to it.
+	reverse_proxy gateway:8080
+
+	# --- Security headers ---
+	header {
+		# HSTS: force HTTPS for two years, include subdomains, allow preload.
+		Strict-Transport-Security "max-age=63072000; includeSubDomains; preload"
+		# Disable MIME sniffing.
+		X-Content-Type-Options "nosniff"
+		# Clickjacking defense (API has no UI, deny framing outright).
+		X-Frame-Options "DENY"
+		# Conservative referrer policy.
+		Referrer-Policy "no-referrer"
+		# Strip server-identifying headers so we don't advertise the stack.
+		-Server
+		-X-Powered-By
+	}
+
+	# Structured access logs to stdout (collected by the container runtime).
+	log {
+		output stdout
+		format json
+	}
+}
+
+# ─────────────────────────────────────────────────────────────────────────────
+# DEV / LOCAL note:
+#
+# For local testing without a public domain or real certificate, replace the
+# site block above with a localhost block that uses Caddy's internal self-signed
+# CA (no Let's Encrypt round-trip):
+#
+#   localhost {
+#       tls internal
+#       reverse_proxy gateway:8080
+#   }
+#
+# Caddy will install its local root CA; trust it or pass `-k` to curl. Note the
+# Phase 1 *dev* compose stack (docker-compose.dev.yml) ships WITHOUT Caddy and
+# exposes the gateway directly on localhost:8080 — this file is for the full
+# production stack only.
+# ─────────────────────────────────────────────────────────────────────────────
+