Refactor feedkit boundaries ahead of v1

Remove global Postgres schema registration in favor of explicit schema-aware sink factory wiring, and update weatherfeeder to register the Postgres sink explicitly. Add optional per-source HTTP timeout and response body limit overrides while keeping feedkit defaults. Remove remaining legacy source/config compatibility surfaces, including singular kind support and old source registry/type aliases, and migrate weatherfeeder sources to plural `Kinds()` metadata. Clean up related docs, tests, and sample config to match the new Postgres, HTTP, and NATS configuration model.

config/config.go

@@ -69,33 +69,25 @@ type SourceConfig struct {
 	// If set, it describes the expected emitted event kinds for this source.
 	Kinds []string `yaml:"kinds"`
 
-	// Kind is the legacy singular form. Prefer "kinds".
-	// If both kind and kinds are set, validation fails.
-	Kind string `yaml:"kind"`
-
 	// Params are driver-specific settings (URL, headers, station IDs, API keys, etc.).
 	// The driver implementation is responsible for reading/validating these.
 	Params map[string]any `yaml:"params"`
 }
 
 // ExpectedKinds returns normalized expected kinds from config.
-// "kinds" takes precedence; "kind" is used as a legacy fallback.
 func (cfg SourceConfig) ExpectedKinds() []string {
-	if len(cfg.Kinds) > 0 {
-		out := make([]string, 0, len(cfg.Kinds))
-		for _, k := range cfg.Kinds {
-			k = strings.TrimSpace(k)
-			if k == "" {
-				continue
-			}
-			out = append(out, k)
+	out := make([]string, 0, len(cfg.Kinds))
+	for _, k := range cfg.Kinds {
+		k = strings.TrimSpace(k)
+		if k == "" {
+			continue
 		}
-		return out
+		out = append(out, k)
 	}
-	if k := strings.TrimSpace(cfg.Kind); k != "" {
-		return []string{k}
+	if len(out) == 0 {
+		return nil
 	}
-	return nil
+	return out
 }
 
 // SinkConfig describes one output sink adapter.