chore: weigh Batocera's pages with its downloads

Batocera's pages now name the cores its x86_64 RetroArch downloads.
Each file lists every core reading it with its citations, the Game
Boy Advance going from 4 readers to 10, and Elektronika BK, FM Towns
and Nintendo DS passed the part budget. On the gate's built site at
27c33b966 the platform weighs 13 pages, 15,662 elements (under the old
18,854) and 1,356,360 bytes, 145,243 more than the 1,211,117 recorded.
The page and byte budgets take those measured values.

tests/test_site_platform_density.py

@@ -262,7 +262,12 @@ class VisibleWordsStayUnderTheirCeiling(unittest.TestCase):
 # elements (outside scripts and styles, as validate_site counts them) and
 # bytes of HTML, on the built site of 2026-10-27.
 BEFORE_WEIGHT = {
-    "batocera": (12, 18_854, 1_211_117),
+    # Batocera's x86_64 RetroArch downloads buildbot cores, which its pages
+    # name since 2026-11-09: each file lists every core that reads it with
+    # its citations (the Game Boy Advance went from 4 readers to 10), and
+    # Elektronika BK, FM Towns and Nintendo DS moved to part pages. Built
+    # site of 27c33b966: 13 pages, 15,662 elements, 1,356,360 bytes.
+    "batocera": (13, 18_854, 1_356_360),
     "amberelec": (1, 7_928, 473_388),
     "romm": (2, 9_561, 572_487),
     "retroarch": (14, 21_503, 1_430_802),