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/rules.go

@@ -154,6 +154,11 @@ func GetDefaultConfig() *Config {
 				Function: "circular_dependency",
 				Message:  "Circular foreign key dependency detected",
 			},
+			"duplicate_index_name": {
+				Enabled:  "enforce",
+				Function: "duplicate_index_name",
+				Message:  "Index name is reused within the schema; PostgreSQL skips the duplicate CREATE INDEX IF NOT EXISTS",
+			},
 		},
 	}
 }