Phase 8a: finish typed indexing — fixeds/ptrs buffers (retire peekf/pokef/peekp/pokep/str_len)

The last peek/poke pairs were the same "typed buffer access wearing a C name" as
peek8/peek32, so they become indexing too:

  peekf(sc_x, i)     -> sc_x[i]        (a `fixeds` buffer -> a fixed)
  pokep(gc_bmp, s,b) -> gc_bmp[s] = b  (a `ptrs` buffer -> a pointer)
  str_len(s)         -> len(s)         (len is polymorphic since 7f; str_len was dead)

Two new element-typed buffers join words: `fixeds` (32-bit fixed) and `ptrs`
(pointer, 8-byte stride). emit_index_addr dispatches on the base type; IR is
byte-identical to the old intrinsics.

The peekf/peekp buffers (ed_x0/ed_x1/ol_x/sc_x fixed coords; gc_bmp/img_px/
tt_data/ui_text pointer arrays) were retyped scope-aware, then the 33 sites
migrated to indexing. Two bugs found via a menu golden diff / a link-time type
error and fixed: the buffer-name regex truncated digit suffixes (ed_x0 -> ed_x),
and the char-literal brace-miscount skipped a few module declarations (same class
as 7j).

Reseeded (22371 lines); C-free fixpoint holds; goldens byte-identical; 18/18;
vocab (fixeds/ptrs types in, 5 intrinsics out) + doc-fences clean.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

selfhost/emit_core.ludic

@@ -54,7 +54,7 @@ fn lbl(pfx: ptr) -> ptr { let r = (pfx + itoa(ll_lbl));  ll_lbl = ll_lbl + 1;  r
 fn llty(t: ptr) -> ptr {
   if (t == "int") or (t == "bool") or (t == "fixed") { return "i32" }
   if (t == "byte") { return "i8" }                # a single byte (p[i] on a raw ptr)
-  if (t == "words") { return "ptr" }              # a 32-bit-word buffer (w[i] is i32)
+  if (t == "words") or (t == "fixeds") or (t == "ptrs") { return "ptr" }   # typed buffers
   if (t == "void") { return "void" }
   return "ptr"
 }