feat: rank console pages above setup lists

A setup's list for one console is a reference page kept out of the
search index, naming its setup as parent. System pages carry file names
and the platforms' own ids as attribute search fields, never as text.
Arcade gets its own sidebar group.

scripts/generate_site.py

@@ -2205,6 +2205,7 @@ def decorate_markdown_pages(docs: Path) -> dict[str, str]:
             description=description, structured=structured, terms=terms,
             search=authored.get("search") != "exclude",
             logo=str(authored.get("logo") or ""),
+            parent=authored.get("parent"),
         )
         write_decorated(docs / target, text)
         # One file per page: a page that gained or lost its components
@@ -7509,12 +7510,19 @@ def _emulator_nav(profiles: dict) -> list:
 
 
 def _system_nav(manufacturers: dict) -> list:
-    """Manufacturer pages, the machines apart from the game and engine trees."""
-    machines, games = [], []
+    """Manufacturer pages, the machines apart from the arcade boards and the
+    game and engine trees: an arcade page's crumb read "Consoles and
+    computers"."""
+    machines, arcade, games = [], [], []
     for mfr in sorted(manufacturers, key=str.casefold):
         entry = {mfr: f"systems/{_slug(mfr)}.md"}
-        (games if mfr in GAME_DATA_TOPS else machines).append(entry)
+        if mfr in GAME_DATA_TOPS:
+            games.append(entry)
+        else:
+            (arcade if mfr == "Arcade" else machines).append(entry)
     nav: list = ["systems/index.md", {"Consoles and computers": machines}]
+    if arcade:
+        nav.append({"Arcade": arcade})
     if games:
         nav.append({"Game engines and PC games": games})
     return nav
@@ -7904,6 +7912,20 @@ def _generate(args: argparse.Namespace) -> None:
             if stem in coverages:
                 raise RuntimeError(f"a system page takes the platform {stem}'s address")
             PART_PAGES.add(f"platforms/{stem}.md")
+            # One console of one setup's list, a reference: "playstation
+            # bios" found five setups' lists before the console's page.
+            # Weighed down, they still won on their title, which the page
+            # weight does not reach, and their file list is already kept out
+            # of the index: the title alone, found again on the setup's page
+            # and the console's, is all the search held of them.
+            SEARCH_DEMOTED.add(f"platforms/{stem}.md")
+            front = _front_matter(page)
+            if front:
+                page = page[page.find("\n---\n", 4) + 5:].lstrip("\n")
+            front.update(level="reference", search="exclude",
+                         parent={"label": cov["platform"], "link": f"{name}.md"})
+            page = "---\n" + yaml.safe_dump(front, sort_keys=False, allow_unicode=True) \
+                + "---\n\n" + page
             write_if_changed(str(docs / "platforms" / f"{stem}.md"), page)
         PAGE_DATA[f"platforms/{name}.md"] = platform_structured_data(name, cov)