feat(pp): COPY TO via std.ch + four PP completeness fixes

`COPY TO <file> [FIELDS <list>] [FOR ...] [WHILE ...] [NEXT ...]
[RECORD ...] [REST] [ALL]` reaches the parser as a plain function
call to a new RTL primitive __dbCopy (rtlDbCopy in hbrtl/database.go).

Implementation: project the field list (case-insensitive name match
against the source's structure, full copy when omitted), dbCreate the
target file with that struct, open it under a temp alias, walk the
source under dbEval-style FOR/WHILE/NEXT/RECORD/REST bounds, and
GetValue/Append/PutValue per record into the target. SDF / DELIMITED
variants stay parser no-ops until those backends arrive.

Wiring up COPY surfaced four longstanding gaps in the PP that had to
be fixed for the rule to even reach the runtime:

  * `<(name)>` *pattern* marker was treated as a regular `<name>`
    with the parens baked into the captured key, so the matching
    result substitution `<(name)>` couldn't find it. parseOneMarker
    now strips the parens at parse time so capture key and result
    marker share the bare name. The smart-stringify result behavior
    is unchanged.
  * matchSegment (the optional-clause matcher) bailed on every
    non-Regular marker. `[FIELDS <fields,...>]` therefore failed to
    match at all and the fields list arrived empty in the result
    template. matchSegment now handles MarkerList with paren-balanced
    capture and segment+outer literal stop boundaries.
  * captureExpression only used the first literal in the pattern
    tail as a stop boundary. With std.ch's chain of optional
    clauses (`[TO <(f)>] [FIELDS ...] [FOR ...] [WHILE ...] ...`)
    the file-name marker was happy to gobble a trailing FOR clause
    when FIELDS was absent. It now stops at *any* of the remaining
    pattern literals.
  * `<(name)>` smart-stringify on a list-typed capture wrapped the
    whole comma-joined string in one set of quotes — `{ "a , b" }` —
    instead of `{ "a", "b" }`. New helper quoteListElements splits on
    top-level commas (paren / bracket / brace / string-balanced) and
    quotes each element. applyResult now consults the rule's marker
    table to know which captures came from `<name,...>`.

Parser cleanup: COPY removed from the IDENT-statement no-op switch in
both parseIdentStmt and parseExprStmt.

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 "COPY", "SORT", "TOTAL", "UPDATE",
+	case "SORT", "TOTAL", "UPDATE",
 		"LABEL", "REPORT", "ACCEPT", "INPUT",
 		"JOIN", "RELEASE", "SAVE", "RESTORE",
 		"DIR", "STORE", "NOTE", "TEXT", "ENDTEXT",