Added automatic pruning for configured Postgres sinks

sinks/doc.go

@@ -29,7 +29,7 @@
 // and feedkit ownership:
 //   - downstream code registers table schema + event mapping functions
 //   - feedkit manages DB connection, create-if-missing DDL, transactional
-//     inserts, and prune helpers
+//     inserts, optional automatic retention pruning, and manual prune helpers
 //
 // Example config:
 //
@@ -40,6 +40,13 @@
 //	      uri: postgres://localhost:5432/feedkit?sslmode=disable
 //	      username: feedkit_user
 //	      password: feedkit_pass
+//	      prune: 3d # optional: prune rows older than now-3d on each write tx
+//
+// params.prune supports:
+//   - Go duration strings (72h, 90m, 30s, ...)
+//   - day/week suffixes (3d, 2w)
+//
+// If params.prune is omitted, automatic pruning is disabled.
 //
 // Example downstream wiring:
 //
@@ -53,7 +60,7 @@
 //	                {Name: "payload_json", Type: "JSONB", Nullable: false},
 //	            },
 //	            PrimaryKey:  []string{"event_id"},
-//	            PruneColumn: "emitted_at",
+//	            PruneColumn: "emitted_at", // required for retention pruning
 //	        },
 //	    },
 //	    MapEvent: func(ctx context.Context, e event.Event) ([]sinks.PostgresWrite, error) {
@@ -74,7 +81,7 @@
 //	    },
 //	})
 //
-// Pruning via type assertion:
+// Manual pruning via type assertion (administrative helpers):
 //
 //	if p, ok := sink.(sinks.PostgresPruner); ok {
 //	    _, _ = p.PruneKeepLatest(ctx, "events", 10000)