sx-pub Phase 1: DB schema, IPFS wiring, actor + webfinger + collections + status endpoints

Foundation for the sx-pub federated publishing protocol:

- 6 SQLAlchemy models: actor, collections, documents, activities, followers, following
- Conditional DB enablement in sx_docs (DATABASE_URL present → enable DB)
- Python IO helpers: get_or_create_actor (auto-generates RSA keypair),
  list_collections, check_status, seed_default_collections
- 4 defhandler endpoints returning text/sx (no JSON):
  /pub/actor, /pub/webfinger, /pub/collections, /pub/status
- Alembic migration infrastructure for sx service
- Docker compose: DB + pgbouncer + IPFS + env vars

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

sx/alembic.ini

@@ -0,0 +1,35 @@
+[alembic]
+script_location = alembic
+sqlalchemy.url =
+
+[loggers]
+keys = root,sqlalchemy,alembic
+
+[handlers]
+keys = console
+
+[formatters]
+keys = generic
+
+[logger_root]
+level = WARN
+handlers = console
+
+[logger_sqlalchemy]
+level = WARN
+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