wcc/ww: flexible rune-const promotion at scalar seams (coercerunelit)

wwstage stamped N_RUNELIT as concrete rune (cstage: untyped_rune,
check.c:1296), so an uncast rune literal into a fitting integer slot
over-rejected where harec accepts (promote_flexible). Add coercerunelit
(mirror of coercefloatlit) at the scalar seams — let-init, return,
call-arg, index-store; coarse accept, no range check (mirror cstage
type.c:379); array-literal elements keep the range gate
(arrlit_init_fits, types.c:923). Teeth: the fnmatch.ww '\\': u8
workaround cast and getopttest's 'X': u8 index-store casts are removed
and compile green. Checker-only (no e.type_ restamp): byte-id held.

lib/fnmatch/fnmatch.ww

@@ -123,8 +123,7 @@ fn pat_next(pat: str, pos: *i32, fl: flag) (u8 | star | question | bracket | end
 			*pos += 1;
 			return c2;
 		};
-		// #29: wwstage over-rejects the implicit flexible-rune-const narrow (harec promote_flexible accepts); explicit cast until flexible-const promotion lands — revert to bare '\\' then.
-		return '\\': u8;
+		return '\\';
 	};
 	return c;
 };