perf(fivesql2): Go-native SqlIsAggName — drop per-row substring scan

B4 GROUP+HAVING profile showed SqlIsAggName at ~9% of CPU —
SqlEvalFunc checks it for every function in every row, and the
PRG body was two string allocations + a substring scan:
  RETURN ("," + c + ",") $ ("," + AGG_FUNCTIONS + ",")

Replace with a hash lookup against the existing aggFuncSet map
in hbrtl/sqlexpr.go (already populated for SqlExprHasAgg, same
AGG_FUNCTIONS list). Upper-casing skips the allocation when the
input is already upper, which it almost always is in practice.

Bench deltas (median of 3 steady runs, 1000 iters):
  B4_GROUP_HAVING 447 → 418 us  -6.5%
  B14_COUNT       252 → 235 us  -7%
  B15_CTE_WIN_JOIN 1595 → 1577 us  -1%
Other benches unchanged (no aggregate calls per row).

FiveSql2 43/43, Harbour compat 56/56.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

hbrtl/register.go

@@ -637,6 +637,7 @@ func RegisterRTL(vm *hbrt.VM) {
 		hbrt.Sym("SQLCOERCENUM", hbrt.FsPublic, SqlCoerceNum),
 		hbrt.Sym("SQLCOERCEFORCMP", hbrt.FsPublic, SqlCoerceForCmp),
 		hbrt.Sym("SQLISTRUE", hbrt.FsPublic, SqlIsTrue),
+		hbrt.Sym("SQLISAGGNAME", hbrt.FsPublic, SqlIsAggName),
 		hbrt.Sym("SQLCMPEQ", hbrt.FsPublic, SqlCmpEq),
 		hbrt.Sym("SQLCMPLT", hbrt.FsPublic, SqlCmpLt),
 		hbrt.Sym("SQLEXTRACTTEMPLATE", hbrt.FsPublic, SqlExtractTemplate),

hbrtl/sqlhelpers.go

@@ -585,3 +585,30 @@ func sqlCmpLt(a, b hbrt.Value) bool {
 	}
 	return false
 }
+
+// SqlIsAggName(cName) → lBool
+// Go-native replacement for TSqlExpr.prg SqlIsAggName. The PRG version
+// was `("," + c + ",") $ ("," + AGG_FUNCTIONS + ",")` — two string
+// allocations + a substring scan per call. Profile showed this at
+// 8.7% of B4 GROUP+HAVING CPU. Uses the aggFuncSet already declared
+// in sqlexpr.go for SqlExprHasAgg.
+func SqlIsAggName(t *hbrt.Thread) {
+	t.Frame(1, 0)
+	defer t.EndProc()
+	name := t.Local(1).AsString()
+	if name == "" {
+		t.RetBool(false)
+		return
+	}
+	// Upper-case without allocating unless needed.
+	upper := name
+	for i := 0; i < len(name); i++ {
+		c := name[i]
+		if c >= 'a' && c <= 'z' {
+			upper = strings.ToUpper(name)
+			break
+		}
+	}
+	_, ok := aggFuncSet[upper]
+	t.RetBool(ok)
+}