parse,check,type,wwi: @packed struct attribute, both stages (#51)

Hare/harec @packed struct layout: no inter-field or trailing padding, align =
max field align (NOT forced to 1) — matches harec type_store.c + types.c:621
(packed{u8,u64}=size 9/align 8). Parser consumes inline @packed (loud-rejects
unknown struct attrs, both stages); layout gates padding on !packed; cstage
type_eq enforces packed type-distinctness; the .wwi producer round-trips
"struct @packed {". wwstage sets slotsize=size for packed so its composite-ABI
copy matches cstage byte-for-byte. cstage identity is faithful; wwstage identity
rides the deferred #224 nominal-resolvealias arc (#108). Both stages byte-id;
447 tests pass.

cmd/wcc/parse.c

@@ -204,8 +204,25 @@ parsetype(Parser *p)
 	}
 	case TK_STRUCT: {
 		advance(p);
-		expect(p, TK_LBRACE);
 		Node *n = newnode(p->a, N_TSTRUCT, pp);
+		/* `@packed` is an inline struct TYPE attribute (harec
+		 * ast.h:95 `bool packed`), sitting after `struct` and
+		 * before `{` — NOT a fn-decl attr, so it does not route
+		 * through parseattrs. */
+		if (p->cur.kind == TK_AT) {
+			advance(p);
+			const char *an = expectident(p);
+			/* p->errs gates the build (cmd/w6c/main.c:82);
+			 * nerrors is advisory-only, so an errorf on a
+			 * clean-recovery path must bump p->errs itself. */
+			if (strcmp(an, "packed") != 0) {
+				errorf(p->cur.pos,
+				    "unknown struct attribute '@%s'", an);
+				p->errs++;
+			} else
+				n->packed = 1;
+		}
+		expect(p, TK_LBRACE);
 		Node *head = NULL, *tail = NULL;
 		while (p->cur.kind != TK_RBRACE && p->cur.kind != TK_EOF) {
 			Pos fp = p->cur.pos;