feat: Harbour RDD parity — NTX/CDX 100% compatible, FIELD-> works

Five RDD engine now matches Harbour DBFNTX and DBFCDX byte-for-byte
in ordering, seek, navigation, and field access. Verified against
Harbour 3.2.0dev with a 281-line comparison test covering:
  - Natural/NAME/CITY/AGE/SALARY/UPPER ordering
  - SEEK (exact/not-found), GoTop/GoBottom per order
  - DELETE/RECALL with SET DELETED
  - CDX compound index read with 5 tags (BYNAME, BYCITY, BYAGE, BYSAL, BYUNAME)
  - Reverse traversal

Fixes:

1. FIELD->NAME returned NIL
   GetAliasField returned interface{} but runtime expected hbrt.Value,
   so the type assertion in PushAliasField failed and pushed NIL.
   - workarea.go: change return type to hbrt.Value, handle FIELD/_FIELD
     as current-workarea alias, add SetAliasField
   - gengo.go: emit SetAliasField() for alias->field := value in both
     statement and expression contexts

2. OrdSetFocus(n) silently switched to natural order
   v.AsString() returns "" for a numeric Value, so OrderListFocus("")
   set current=-1.
   - indexrtl.go: convert numeric param via fmt.Sprintf("%d", ...)

3. CDX compound tag order mismatched Harbour
   Five decoded the structural B-tree which is alphabetical, but
   Harbour sorts tags by TagBlock (file offset = creation order).
   - cdx/cdx.go: sort tagEntries by offset ascending after decoding,
     matching hb_cdxIndexLoadAvailTags in dbfcdx1.c

4. OutStd()/OutErr() not registered — caused panic on call
   - hbrtl/console.go: add rtlOutStd/rtlOutErr implementations
   - hbrtl/register.go: register OUTSTD and OUTERR
   - analyzer.go: add OUTSTD/OUTERR to RTL known-functions

5. FIELD keyword triggered "undeclared variable" warnings
   - analyzer.go: add FIELD, _FIELD, M, MEMVAR as builtin constants

Tests:
  go test ./...        — ALL PASS (17 packages)
  FiveSql2 43/43       — 100%
  compat_harbour 51/51 — 100%
  Harbour diff         — 0 lines differ (281-line comparison)

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

hbrdd/cdx/cdx.go

@@ -22,6 +22,7 @@ import (
 	"encoding/binary"
 	"fmt"
 	"os"
+	"sort"
 	"strings"
 	"syscall"
 )
@@ -376,6 +377,14 @@ func OpenIndex(path string) (*Index, error) {
 	// points to the tag header at a specific file offset.
 	tagEntries := readCompoundTagList(idx, rootHdr)
 
+	// Harbour orders tags by file offset (TagBlock) ascending, which
+	// corresponds to creation order. The compound B-tree stores entries
+	// alphabetically, so we must re-sort by offset to match Harbour.
+	// See: hb_cdxIndexLoadAvailTags in dbfcdx1.c
+	sort.Slice(tagEntries, func(i, j int) bool {
+		return tagEntries[i].offset < tagEntries[j].offset
+	})
+
 	for _, entry := range tagEntries {
 		tagHdr, err := ReadTagHeader(f, entry.offset)
 		if err != nil {

hbrdd/workarea.go

@@ -9,6 +9,7 @@
 package hbrdd
 
 import (
+	"five/hbrt"
 	"fmt"
 	"strings"
 )
@@ -213,11 +214,18 @@ func (wm *WorkAreaManager) CloseAll() {
 }
 
 // GetAliasField returns a field value from a named alias.
-// Used by alias->field syntax.
-func (wm *WorkAreaManager) GetAliasField(alias, field string) interface{} {
-	area := wm.ByAlias(alias)
+// Used by alias->field syntax (e.g., CUSTOMERS->NAME, FIELD->AGE).
+func (wm *WorkAreaManager) GetAliasField(alias, field string) hbrt.Value {
+	var area Area
+
+	// FIELD-> is a special alias meaning "current workarea"
+	if strings.EqualFold(alias, "FIELD") || strings.EqualFold(alias, "_FIELD") {
+		area = wm.Current()
+	} else {
+		area = wm.ByAlias(alias)
+	}
 	if area == nil {
-		return nil
+		return hbrt.MakeNil()
 	}
 	// Find field by name
 	for i := 0; i < area.FieldCount(); i++ {
@@ -227,7 +235,28 @@ func (wm *WorkAreaManager) GetAliasField(alias, field string) interface{} {
 			return val
 		}
 	}
-	return nil
+	return hbrt.MakeNil()
+}
+
+// SetAliasField sets a field value by alias->field syntax.
+func (wm *WorkAreaManager) SetAliasField(alias, field string, val hbrt.Value) {
+	var area Area
+
+	if strings.EqualFold(alias, "FIELD") || strings.EqualFold(alias, "_FIELD") {
+		area = wm.Current()
+	} else {
+		area = wm.ByAlias(alias)
+	}
+	if area == nil {
+		return
+	}
+	for i := 0; i < area.FieldCount(); i++ {
+		fi := area.GetFieldInfo(i)
+		if strings.EqualFold(fi.Name, field) {
+			area.PutValue(i, val)
+			return
+		}
+	}
 }
 
 // --- Helpers ---