feat(pgsql): diff against the live database by default for direct output

Direct pgsql output (job output.conn_env, merge --output-conn) now reads the live
schema and executes only the differences. full_ddl: true (job option) or --full-ddl
(merge) restores the full idempotent DDL; file output is unchanged.

- compare PKs by columns, skip constraint-backed indexes, normalize index method,
  FK actions, serial/numeric types, default literals/casts and truncated names
- diff table and column comments instead of re-emitting them
- remove leftover ZZDUMP debug code

pkg/writers/pgsql/migration_writer.go

@@ -1,6 +1,8 @@
 package pgsql
 
 import (
+	"bytes"
+	"encoding/json"
 	"fmt"
 	"io"
 	"os"
@@ -1044,9 +1046,57 @@ func normalizeDefaultLiteral(s string) string {
 		if end := strings.LastIndex(s, "'"); end > 0 {
 			rest := strings.TrimSpace(s[end+1:])
 			if rest == "" || strings.HasPrefix(rest, "::") {
-				return strings.ReplaceAll(s[1:end], "''", "'")
+				return normalizeJSONLiteral(strings.ReplaceAll(s[1:end], "''", "'"))
 			}
 		}
+		return s
+	}
+	if strings.HasPrefix(s, "(") && strings.Contains(s, ")::") {
+		return normalizeCastExpression(s)
+	}
+	return normalizeJSONLiteral(s)
+}
+
+// normalizeJSONLiteral compacts JSON text, since jsonb reports defaults re-spaced
+// ('["a", "b"]') while the model usually holds them minified.
+func normalizeJSONLiteral(s string) string {
+	if !strings.HasPrefix(s, "[") && !strings.HasPrefix(s, "{") {
+		return s
+	}
+	var buf bytes.Buffer
+	if err := json.Compact(&buf, []byte(s)); err != nil {
+		return s
+	}
+	return buf.String()
+}
+
+// normalizeCastExpression strips whitespace and the redundant parentheses PostgreSQL adds
+// around an expression it casts: (gen_random_uuid())::text -> gen_random_uuid()::text.
+func normalizeCastExpression(s string) string {
+	s = strings.Join(strings.Fields(s), "")
+	for strings.HasPrefix(s, "(") {
+		end := strings.LastIndex(s, ")::")
+		if end < 0 {
+			break
+		}
+		inner := s[1:end]
+		depth := 0
+		balanced := true
+		for _, r := range inner {
+			if r == '(' {
+				depth++
+			} else if r == ')' {
+				depth--
+				if depth < 0 {
+					balanced = false
+					break
+				}
+			}
+		}
+		if !balanced || depth != 0 {
+			break
+		}
+		s = inner + s[end+1:]
 	}
 	return s
 }