fix: 3 RDD compat bugs — FIELD->, AsNumInt Double, PACK/ZAP with index

Bug 1: FIELD->NAME in INDEX ON expression
- evalKeyExprInner: strip FIELD->/alias-> prefix before field lookup
- exprToString: handle AliasExpr (FIELD->NAME → "FIELD->NAME")

Bug 2: AsNumInt() on Double returned IEEE 754 raw bits
- Value.AsNumInt(): check tDouble and convert via Float64frombits
- Fixed array index crash when index is result of % modulo

Bug 3: PACK/ZAP crash with open indexes
- OrderListRebuild: fully implemented (was TODO stub)
  Saves index info, closes all, sets idxState=nil, recreates
- OrderCreate: set current=-1 during key evaluation (natural GoTo)
- PACK/ZAP: save/restore idxState, rebuild after operation
- Register __DBPACK, __DBZAP, DBRECALL symbol aliases

Harbour vs Five: 45/47 match (96%), 2 diffs are duplicate-key sort order

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

hbrt/value.go

@@ -155,7 +155,12 @@ func (v Value) AsLong() int64      { return int64(v.scalar) }
 func (v Value) AsDouble() float64  { return math.Float64frombits(v.scalar) }
 func (v Value) AsJulian() int64    { return int64(v.scalar) }
 func (v Value) AsTimeMs() int32    { return int32(v.info & auxMask) }
-func (v Value) AsNumInt() int64    { return int64(v.scalar) }
+func (v Value) AsNumInt() int64 {
+	if v.Type() == tDouble {
+		return int64(math.Float64frombits(v.scalar))
+	}
+	return int64(v.scalar)
+}
 
 // AsNumDouble returns a double value from any numeric type.
 func (v Value) AsNumDouble() float64 {