erlang: fold lists/proplists stdlib BIFs into transpile.sx + runtime.sx (874/874)

Brings the loops/erlang stdlib hardening into the canonical files so
every erlang consumer (fed-sx, identity, ...) gets them — not just a
separate conformance-only file.

lists: sort/1,2 usort/1 keyfind/keymember/keydelete/keyreplace/keystore/
keytake/keysort foldr partition takewhile dropwhile splitwith flatten
max min zip zipwith unzip sublist/2,3 nthtail split droplast flatmap
filtermap mapfoldl search.
proplists: get_value/2,3 get_all_values is_defined lookup delete.

Impls appended to transpile.sx; registrations added directly inside
er-register-builtin-bifs! (so they survive the registry resets that
tests/runtime.sx performs — no wrapper needed when folded in). Full
term order via self-contained er-ext-lt? (the shared er-lt? does not
deep-compare tuples/lists). New lists_ext suite wired into
conformance.conf (dict mode). Conformance 771 -> 874/874.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/erlang/scoreboard.md

@@ -1,6 +1,6 @@
 # Erlang-on-SX Scoreboard
 
-**Total: 771 / 771 tests passing**
+**Total: 874 / 874 tests passing**
 
 |  | Suite | Pass | Total |
 |---|---|---|---|
@@ -16,5 +16,6 @@
 | ✅ | ffi | 37 | 37 |
 | ✅ | vm | 78 | 78 |
 | ✅ | send_after | 10 | 10 |
+| ✅ | lists_ext | 103 | 103 |
 
 Generated by `lib/erlang/conformance.sh`.