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/validate_test.go

@@ -114,31 +114,6 @@ func TestValidate_SourceModeRejectsUnknownValue(t *testing.T) {
 	}
 }
 
-func TestValidate_SourceKindAndKindsConflict(t *testing.T) {
-	cfg := &Config{
-		Sources: []SourceConfig{
-			{
-				Name:   "src1",
-				Driver: "driver1",
-				Every:  Duration{Duration: time.Minute},
-				Kind:   "observation",
-				Kinds:  []string{"forecast"},
-			},
-		},
-		Sinks: []SinkConfig{
-			{Name: "sink1", Driver: "stdout"},
-		},
-	}
-
-	err := cfg.Validate()
-	if err == nil {
-		t.Fatalf("expected error, got nil")
-	}
-	if !strings.Contains(err.Error(), `sources[0].kind`) {
-		t.Fatalf("expected error to mention sources[0].kind, got: %v", err)
-	}
-}
-
 func TestValidate_SourceKindsRejectBlankEntries(t *testing.T) {
 	cfg := &Config{
 		Sources: []SourceConfig{