Perf: composite (event_type, timestamp) index + test-schema sweep + README

DB latency: every projection runs `WHERE event_type=? ORDER BY timestamp DESC
LIMIT n`. With only a plain timestamp index, the latest of a STALE type
backward-scans the whole events table — measured 373ms / ~52k buffers on 235k
rows. Add a composite index in event_store._ensure_schema:

    CREATE INDEX idx_events_type_ts ON events(event_type, timestamp DESC)

-> same query is now a 0.018ms index seek (3 buffers). Applied to the live DB
CONCURRENTLY; also dropped two redundant legacy indexes (idx_events_type, now
covered by the composite prefix; idx_events_correlation, a dup of
idx_events_session_id) to cut write overhead.

tests/conftest.py: sweep the throwaway `mem_*` schemas EventStore(":memory:")
creates — 170 had leaked into the shared Postgres, bloating the catalog.

README: rewritten around the current system — PostgreSQL event store, a full
command reference (run_live_paper / momentum CLI / eod_replay / sweeps / tuning /
cron), config knobs, and a database & performance section (the index above,
extension guidance, retention).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/conftest.py

@@ -0,0 +1,38 @@
+"""Shared pytest fixtures + session cleanup.
+
+Drop the throwaway ``mem_*`` schemas that ``EventStore(":memory:")`` creates for
+test isolation. The closing fixture drops them on ``.close()``, but tests that
+build a store inline (without that fixture) leak one schema per run — 170 had
+piled up in the shared Postgres instance, bloating the catalog and slowing
+query planning. This sweeps them at session end.
+"""
+
+import os
+
+import pytest
+
+
+@pytest.fixture(scope="session", autouse=True)
+def _drop_leftover_mem_schemas():
+    yield  # run after the whole session
+    # Under xdist each worker shares the same Postgres, so a worker dropping at
+    # its own session-end could yank a schema another worker is still using.
+    # Only sweep in serial runs (the common case); parallel runs can sweep
+    # manually afterwards.
+    if os.environ.get("PYTEST_XDIST_WORKER"):
+        return
+    url = os.environ.get("DATABASE_URL")
+    if not url:
+        return
+    try:
+        import psycopg2
+        conn = psycopg2.connect(url)
+        conn.autocommit = True
+        cur = conn.cursor()
+        cur.execute("SELECT schema_name FROM information_schema.schemata "
+                    "WHERE schema_name LIKE 'mem_%'")
+        for (schema,) in cur.fetchall():
+            cur.execute(f'DROP SCHEMA IF EXISTS "{schema}" CASCADE')
+        conn.close()
+    except Exception:  # noqa: BLE001 — cleanup must never fail the run
+        pass