w6c: fold dot chains through inferred-alloc struct pointers (#24 residue)

wwstage dotchainresolve gated its *T roots on an N_TPTR-over-N_TNAME
tnode; an inferred `let p = alloc(S{...})!` rides the checker-
SYNTHESIZED N_TPTR whose pointee is the struct BODY node (the #24
TNAME-normalize covers only the direct struct-lit binding), so the
root gate failed and chained p.field.pseudo reads fell to the
unfused deref arms — shape-only divergence vs cstage's type-keyed
fold (both stages runtime-correct; the historical field(SB) leak the
pin described was already fixed). Widen the local and global root
gates to accept the N_TSTRUCT pointee; correctness stays enforced by
the stamped-tinfo peel below (TY_PTR -> pointee TY_STRUCT).

Graduates alias_g73_heapfill out of DATABYTEID_DIVERGED (2 pins
remain, both the tagged-spill family); adds compile fixtures pinning
the newly-converged siblings (nested read+store, slice .cap,
inferred-global root; pin 1730/22/3460) and a runtime lang row that
mutates then re-points the heap base — a read bypassing the pointer
returns the wrong len.

test/wcc/data/alias_g73_heapfill/case.ww

@@ -1,5 +1,5 @@
 //ww:compile
-// migrated from test/wcc/944_alias_cgen_b5_run.c: heap struct-lit str-arm fill through a 2-level str alias — pins the absence of the pre-c2 cstage #73 fatal; ww .s carries the #24 field(SB) deref-read leak (DATABYTEID_DIVERGED).
+// migrated from test/wcc/944_alias_cgen_b5_run.c: heap struct-lit str-arm fill through a 2-level str alias — pins the absence of the pre-c2 cstage #73 fatal AND the chained deref-read fold through an inferred alloc pointer (the historical #24 field(SB) leak's residue; byte-id since the dotchainresolve N_TSTRUCT-pointee gate).
 package main;
 type s1t = str;
 type s2t = s1t;