lib/ww/syntax: export the 16 public types consumed by the wcc backend (#72)

After the frontend consolidated into one syntax package, the wcc backend
imports syntax and calls its exported fns — whose signatures reference
types that were unexported. Producing syntax's .wwi interface re-triggered
check_exported_type ("exported declaration references unexported type"):
the residual of BUG-A at the one surviving syntax->wcc boundary. Export
the 16 types that appear in syntax's wcc-facing public surface (directly
in an exported signature, or via a recursively-referenced exported struct
field): nkind, node, lex, tok, tkind, parser, scope, sym, skind, tinfo,
tykind, tfield, tparam, ttupleelem, tctx, tinfocacheent. The set is
minimal (unexporting any one re-breaks the producer) and complete; pos
stays internal. Pure source change — exporting a type emits no code, so
the bootstrap binaries are byte-identical (verified against a clean base
build); only syntax's .wwi gains the type decls.

Post-frontend-reorg residual (#74). syntax now sep-produces clean both
stages. The separate concern of wcc's currently-unqualified refs to
syntax symbols (#75) is a distinct follow-up. Gate 989_syntaxexport_run.

lib/ww/syntax/ast.ww

@@ -21,7 +21,7 @@ import strconv;
 // explicit and must stay in sync — the 990_selfhost test diffs
 // astprint against the C side byte-for-byte. Tail-appended entries
 // (TYPETEST onward) preserve every prior N_* value.
-type nkind = enum i32 {
+export type nkind = enum i32 {
 	N_NONE     = 0,
 
 	N_INTLIT   = 1,
@@ -115,7 +115,7 @@ type nkind = enum i32 {
 
 // ---- Node -------------------------------------------------------------
 
-type node = struct {
+export type node = struct {
 	kind:    nkind,
 	file:    str,
 	line:    i32,

lib/ww/syntax/lex.ww

@@ -46,7 +46,7 @@ fn hexval(c: rune) (i32 | void) = {
 	return;
 };
 
-type lex = struct {
+export type lex = struct {
 	file:   str,
 	src:    *u8,	// raw bytes; not necessarily NUL-terminated
 	srclen: u64,

lib/ww/syntax/parse.ww

@@ -17,7 +17,7 @@ package syntax;
 import os;
 import strings;
 
-type parser = struct {
+export type parser = struct {
 	l:    *lex,
 	errs: i32,
 	// nocast: while inside `[...]` we treat ':' as the slice

lib/ww/syntax/sym.ww

@@ -7,7 +7,7 @@
 package syntax;
 
 // Symbol kinds — must stay numerically aligned with cmd/wcc/ww.h Skind.
-type skind = enum i32 {
+export type skind = enum i32 {
 	SK_NONE  = 0,
 	SK_VAR   = 1,
 	SK_PARAM = 2,
@@ -18,7 +18,7 @@ type skind = enum i32 {
 	SK_FIELD = 7,
 };
 
-type sym = struct {
+export type sym = struct {
 	name:     str,
 	skind:    skind,
 	type_:    *tinfo,
@@ -43,7 +43,7 @@ type sym = struct {
 
 def NBUCKETS: i32 = 16;
 
-type scope = struct {
+export type scope = struct {
 	parent:   *scope,
 	first:    *sym,
 	last:     *sym,

lib/ww/syntax/tok.ww

@@ -20,7 +20,7 @@ import strings;
 // explicit and must stay in sync — the 990_selfhost test diffs wwdump
 // output against the C side, byte for byte.
 
-type tkind = enum i32 {
+export type tkind = enum i32 {
 	TK_NONE     = 0,
 	TK_EOF      = 1,
 	TK_ERR      = 2,
@@ -143,7 +143,7 @@ type pos = struct {
 	col:  i32,
 };
 
-type tok = struct {
+export type tok = struct {
 	kind: tkind,
 	file: str,	// path of the source the token came from
 	line: i32,

lib/ww/syntax/typ.ww

@@ -18,7 +18,7 @@ import os;
 // Mirror of the C `TypeKind` enum in cmd/wcc/ww.h. Numeric values
 // are explicit and must stay in sync — the selfhost selfcheck and
 // typed-AST printers depend on matching numeric layout.
-type tykind = enum i32 {
+export type tykind = enum i32 {
 	TY_NONE     = 0,
 	TY_VOID     = 1,
 	TY_BOOL     = 2,
@@ -69,14 +69,14 @@ def SIZE_UNDEFINED: u64 = 18446744073709551615;
 
 // ---- tinfo / tfield / tparam -----------------------------------------
 
-type tfield = struct {
+export type tfield = struct {
 	name:   str,
 	type_:  *tinfo,
 	offset: u64,
 	tnext:  *tfield,
 };
 
-type tparam = struct {
+export type tparam = struct {
 	name:   str,
 	type_:  *tinfo,
 	// #61a: per-variant `!T` error mark for TY_TAGGED variants.
@@ -98,13 +98,13 @@ type tparam = struct {
 // sea-of-stars mirrors Hare's structural choice; the empty-name idiom
 // from #50's TTAGGED-on-tparam would conflate two semantic axes
 // (variants can be named; positionals never can).
-type ttupleelem = struct {
+export type ttupleelem = struct {
 	type_:  *tinfo,
 	offset: u64,
 	tnext:  *ttupleelem,
 };
 
-type tinfo = struct {
+export type tinfo = struct {
 	kind: tykind,
 	size:     u64,
 	align:    u64,
@@ -154,7 +154,7 @@ type tinfo = struct {
 // (rule-12): cnext chains WITHIN a bucket; lookup/bind hash then touch
 // only one bucket -> O(1) amortized. Identical lookup results (same
 // *tinfo for the same node), so emitted asm is byte-identical.
-type tinfocacheent = struct {
+export type tinfocacheent = struct {
 	key:    *node,
 	val:    *tinfo,
 	cnext:  *tinfocacheent,
@@ -168,7 +168,7 @@ def NBUCKETS_TINFO: u64 = 8192u64;
 
 // ---- tctx — the box of primitive types -------------------------------
 
-type tctx = struct {
+export type tctx = struct {
 	tyvoid:  *tinfo,
 	tybool:  *tinfo,
 	tyrune:  *tinfo,