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).

alembic.ini

@@ -0,0 +1,49 @@
+# Alembic configuration for neuronetz-gateway.
+# The database URL is read from the DATABASE_URL environment variable in
+# alembic/env.py (do not hardcode credentials here).
+
+[alembic]
+script_location = alembic
+prepend_sys_path = src
+version_path_separator = os
+# version_locations defaults to alembic/versions
+
+# DATABASE_URL is injected at runtime; this placeholder is never used directly.
+sqlalchemy.url = driver://user:pass@localhost/dbname
+
+[post_write_hooks]
+# (none)
+
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARNING
+handlers = console
+qualname =
+
+[logger_sqlalchemy]
+level = WARNING
+handlers =
+qualname = sqlalchemy.engine
+
+[logger_alembic]
+level = INFO
+handlers =
+qualname = alembic
+
+[handler_console]
+class = StreamHandler
+args = (sys.stderr,)
+level = NOTSET
+formatter = generic
+
+[formatter_generic]
+format = %(levelname)-5.5s [%(name)s] %(message)s
+datefmt = %H:%M:%S