Added support for Postgres polling sources

sources/doc.go

@@ -9,6 +9,8 @@
 //     stream exit classification helpers
 //   - Registry / NewRegistry: source driver registry and builders
 //   - HTTPSource / NewHTTPSource: reusable HTTP polling helper
+//   - PostgresQuerySource / NewPostgresQuerySource: reusable Postgres polling
+//     helper
 //
 // Source drivers are domain-specific and registered into Registry by driver name.
 // Registry can then build configured sources from config.SourceConfig.
@@ -34,4 +36,17 @@
 // When validators are available, NewHTTPSource prefers ETag/If-None-Match and
 // falls back to Last-Modified/If-Modified-Since. A 304 Not Modified response is
 // treated as a successful unchanged poll.
+//
+// Postgres-backed polling sources can share NewPostgresQuerySource for generic
+// DB config parsing and query execution. The helper understands:
+//   - params.uri
+//   - params.username
+//   - params.password
+//   - params.query
+//   - params.query_timeout (optional, default 30s)
+//
+// feedkit does not register a built-in postgres poll driver. Downstream daemons
+// should register domain-specific driver names that call
+// NewPostgresQuerySource, then keep SQL semantics, row scanning, ordering,
+// watermark policy, and event construction in their own source types.
 package sources