wcc: forrange bindings get a per-loop scope; dup binders reject

The TODO(#11) silent-accept of `for (let (a, a) .. xs)` rested on a
stale premise -- resolvewalk has per-block scopes since #53 and IS
the live w6c_ww checker pass. Bindings now install in a per-LOOP
scope (the N_MCASE pattern), so a duplicate name within one pattern
errs "redeclared in same scope" (cstage parity via stamptuplebinds'
scopedefine-nil check) while sequential same-name loops stay legal.
kwtab restores its stated alphabetical order (`import` before `is`,
both stages, kinds swapped in lockstep with names).

lib/ww/syntax/tok.ww

@@ -156,16 +156,16 @@ export type tok = struct {
 // (probe at cc69daf — len() returns 0, no diagnostic); filed bug.
 let kwnames: [30]str = [
 	"as", "break", "case", "chan", "const", "continue", "def", "defer",
-	"else", "enum", "export", "false", "fn", "for", "if", "is",
-	"import", "let", "match", "nil", "package", "proc", "return",
+	"else", "enum", "export", "false", "fn", "for", "if", "import",
+	"is", "let", "match", "nil", "package", "proc", "return",
 	"static", "struct", "switch", "true", "type", "void", "yield",
 ];
 let kwkinds: [30]tkind = [
 	tkind.TK_AS, tkind.TK_BREAK, tkind.TK_CASE, tkind.TK_CHAN,
 	tkind.TK_CONST, tkind.TK_CONTINUE, tkind.TK_DEF, tkind.TK_DEFER,
 	tkind.TK_ELSE, tkind.TK_ENUM, tkind.TK_EXPORT, tkind.TK_FALSE,
-	tkind.TK_FN, tkind.TK_FOR, tkind.TK_IF, tkind.TK_IS,
-	tkind.TK_USE, tkind.TK_LET, tkind.TK_MATCH, tkind.TK_NIL,
+	tkind.TK_FN, tkind.TK_FOR, tkind.TK_IF, tkind.TK_USE,
+	tkind.TK_IS, tkind.TK_LET, tkind.TK_MATCH, tkind.TK_NIL,
 	tkind.TK_MODULE, tkind.TK_PROC, tkind.TK_RETURN, tkind.TK_STATIC,
 	tkind.TK_STRUCT, tkind.TK_SWITCH, tkind.TK_TRUE, tkind.TK_TYPE,
 	tkind.TK_VOID, tkind.TK_YIELD,