feat(inspector): fail on duplicate index names per schema

PostgreSQL index names share the schema-wide relation namespace, so a
reused name makes CREATE INDEX IF NOT EXISTS silently skip the duplicate.
Add duplicate_index_name rule (enforce by default) covering indexes and
PK/unique constraint backing indexes.

pkg/inspector/validators.go

@@ -643,3 +643,64 @@ func contains(slice []string, value string) bool {
 	}
 	return false
 }
+
+// validateDuplicateIndexName checks that index names are unique per schema.
+// PostgreSQL keeps indexes in the schema-wide relation namespace, so a name
+// reused on another table makes CREATE INDEX IF NOT EXISTS silently skip it.
+// Primary key and unique constraints create backing indexes and share that
+// namespace too. An index and a constraint with the same name on the same
+// table describe one object and are not reported.
+func validateDuplicateIndexName(db *models.Database, rule Rule, ruleName string) []ValidationResult {
+	results := []ValidationResult{}
+
+	for _, schema := range db.Schemas {
+		// lowercased name -> "table" entries, one per distinct object
+		owners := make(map[string][]string)
+		display := make(map[string]string)
+		order := []string{}
+
+		add := func(name, table string, sameTableMerges bool) {
+			key := strings.ToLower(name)
+			if _, seen := owners[key]; !seen {
+				order = append(order, key)
+				display[key] = name
+			}
+			if sameTableMerges && contains(owners[key], table) {
+				return
+			}
+			owners[key] = append(owners[key], table)
+		}
+
+		for _, table := range schema.Tables {
+			for _, key := range sortedKeys(table.Indexes) {
+				if name := table.Indexes[key].Name; name != "" {
+					add(name, table.Name, false)
+				}
+			}
+			for _, c := range sortConstraints(table.Constraints) {
+				if c.Name == "" || (c.Type != models.PrimaryKeyConstraint && c.Type != models.UniqueConstraint) {
+					continue
+				}
+				add(c.Name, table.Name, true)
+			}
+		}
+
+		for _, key := range order {
+			tables := owners[key]
+			results = append(results, createResult(
+				ruleName,
+				len(tables) == 1,
+				rule.Message,
+				formatLocation(schema.Name, display[key], "")+" on "+strings.Join(tables, ", "),
+				map[string]interface{}{
+					"schema":      schema.Name,
+					"index":       display[key],
+					"tables":      tables,
+					"occurrences": len(tables),
+				},
+			))
+		}
+	}
+
+	return results
+}