fix(0117): pointer-to-array indexing auto-derefs

A '*[N]T' receiver in an index expression reached LLVM emission with an
unresolved element type and tripped the panic sentinel — no read or
write spelling worked. ptrToArrayElem on Lowering recognises the shape;
the index READ path GEPs the pointee array through the pointer value
and loads the element; the write / compound-assign / lvalue /
addr-of-element paths and the expression typer resolve the element type
through the same helper (their GEP machinery already handled a pointer
base). Kept out of getElementType so slice paths don't half-accept a
raw pointer base.

Regression: examples/0176 (read, write, compound, element ptr + deref).

examples/expected/0176-types-pointer-to-array-index.exit

@@ -0,0 +1 @@
+0

examples/expected/0176-types-pointer-to-array-index.stderr

@@ -0,0 +1 @@
+

examples/expected/0176-types-pointer-to-array-index.stdout

@@ -0,0 +1,3 @@
+read=33
+write=99 99 45
+elem-ptr=33