Add D1 migration baseline

cloudflare/migrations/0005_audit.sql

@@ -0,0 +1,17 @@
+CREATE TABLE IF NOT EXISTS audit_events (
+  event_id TEXT PRIMARY KEY,
+  user_id TEXT,
+  actor_device_id TEXT,
+  event_type TEXT NOT NULL,
+  subject_type TEXT NOT NULL,
+  subject_id TEXT,
+  outcome TEXT NOT NULL CHECK (outcome IN ('success', 'failure', 'denied')),
+  metadata_hash TEXT,
+  created_at INTEGER NOT NULL
+);
+
+CREATE INDEX IF NOT EXISTS idx_audit_events_user_time
+  ON audit_events (user_id, created_at);
+
+CREATE INDEX IF NOT EXISTS idx_audit_events_type_time
+  ON audit_events (event_type, created_at);