ww/lex: fold float literals through strconv.stof64 — 1-ULP cs≠ww class (#62)

wwstage's parsef64 (naive i64-accumulator + pow-10 fold) diverged from
cstage's strtod: >19-digit mantissas overflowed the accumulator (sign-bit
garbage), DBL_MIN was +1 ULP, DBL_MAX -2 ULP — the #59.10 ratchet pin.
C-strtod oracle confirms cstage correctly rounded on every vector, so
wwstage aligns to it by dogfooding strconv.stof64 (correctly-rounded
decimal engine, already imported by lex.ww). Overflow literals now
reject in both stages (stof64 overflow -> errat, mirroring ERANGE).

Fix + #59.10 M_DIVERGE->M_ID graduation + pins land together per the
ratchet's designed flow (the gate trips loud demanding graduation):
oracle-pinned vectors in toktest.ww floatfold_cases (lexer-unit) and
989_floatlit_run (compiler fold: runtime bits + byte-id + overflow
reject parity). Retained subnormal accept-set asymmetry filed as task
#21, documented at the lexnum site.

Makefile

@@ -427,6 +427,7 @@ TESTS	= $(BIN)/test_smoke $(BIN)/test_lex $(BIN)/test_parse $(BIN)/test_check \
 	  $(BIN)/test_siphash_run $(BIN)/test_sha256_run \
 	  $(BIN)/test_regex_run \
 	  $(BIN)/test_lib_byteid \
+	  $(BIN)/test_floatlit_run \
 	  $(BIN)/test_checked_run \
 	  $(BIN)/test_floatarr_run \
 	  $(BIN)/test_deref_narrow_run \
@@ -1830,6 +1831,10 @@ $(BIN)/test_lib_byteid: test/wcc/989_lib_byteid.c $(BIN)/ww $(BIN)/w6c \
 		$(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<
 
+$(BIN)/test_floatlit_run: test/wcc/989_floatlit_run.c $(BIN)/ww $(BIN)/w6c \
+		$(BIN)/w6c_ww $(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
+	$(CC) $(CFLAGS) -o $@ $<
+
 $(BIN)/test_bufio_run: test/wcc/998_bufio_run.c $(BIN)/ww $(BIN)/w6c \
 		$(BIN)/w6a $(BIN)/w6l $(LIB)/libwwrt.a | $(BIN)
 	$(CC) $(CFLAGS) -o $@ $<