feat(pp): TOTAL TO via std.ch + __dbTotal RTL

`TOTAL TO <file> ON <key> [FIELDS <list>] [FOR ...] [WHILE ...]
[NEXT ...] [RECORD ...] [REST] [ALL]` joins the family of std.ch
DML rewrites. New RTL primitive __dbTotal:

  * Walk the source under dbEval-style FOR/WHILE/NEXT/RECORD/REST
    bounds. The source must already be sorted/indexed on the key —
    same precondition as Harbour's dbtotal.prg.
  * Track the current group key. On each key change, flush the
    accumulated row to the destination (writing the running totals
    back into the most recently appended record's sum-fields,
    preserving each field's declared length/decimals).
  * On the *first* record of every group, append a fresh dst row
    and copy all non-memo source fields into it; subsequent records
    in the group only contribute to the sums. Net effect: non-summed
    fields take the first record's value, summed fields hold the
    group total. Same shape as harbour-core/src/rdd/dbtotal.prg.
  * Memo fields are dropped from the destination structure (Harbour
    does the same).

Parser cleanup: TOTAL removed from the IDENT-statement no-op switch.

Gates green:
  go test ./...      : PASS
  FiveSql2 SQL:1999  : 43/43
  Harbour compat     : 56/56

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

compiler/parser/parser.go

@@ -1155,7 +1155,7 @@ func (p *Parser) parseIdentStmt() ast.Stmt {
 	// rewritten by compiler/pp/std.ch into function calls before the
 	// parser sees them.
 	switch upper {
-	case "TOTAL", "UPDATE",
+	case "UPDATE",
 		"LABEL", "REPORT", "ACCEPT", "INPUT",
 		"JOIN", "RELEASE", "SAVE", "RESTORE",
 		"DIR", "STORE", "NOTE", "TEXT", "ENDTEXT",