fix: describe platform pages by what they give

The meta description of each platform page was its summary followed by the label of a link, "ROCKNIX website.", and never said the page gives the BIOS files, their folder and the install command.

scripts/generate_site.py

@@ -2516,6 +2516,12 @@ def _page_description(markdown: str, relative: Path, title: str) -> str:
         return _system_description(markdown, browser)
     if key.startswith("emulators/") and relative.stem != "index":
         return _emulator_description(markdown, key, title, _first_paragraph(lead))
+    if key.startswith("platforms/") and relative.stem != "index":
+        # The summary ends on a link to the platform's site, whose label
+        # alone was left: "A system for handhelds. ROCKNIX website."
+        summary = _first_paragraph(lead).removesuffix(f" {title} website.")
+        return _shorten(f"The BIOS files for {title}, the folder they go in and the "
+                        f"command that installs them. {summary}", 155)
     first = _first_paragraph(lead, minimum=35)
     questions = [_plain_markdown(re.sub(r"\s*\{[^}]*\}\s*$", "", heading))
                  for heading in re.findall(r"^## (.+\?)(?:[ \t]*\{[^}]*\})?[ \t]*$", markdown, re.M)]

tests/test_site_search.py

@@ -245,6 +245,16 @@ class Descriptions(unittest.TestCase):
         self.assertEqual(gs._page_description(body, key, "DaedalusX64"),
                          "DaedalusX64 emulates Nintendo 64. Every file it reads comes with the app.")
 
+    def test_a_platform_page_says_what_it_gives(self) -> None:
+        """All 18 ended on the label of a link a snippet cannot follow,
+        "ROCKNIX website.", and never named the BIOS files or their folder."""
+        body = ("# ROCKNIX\n\nA system for handhelds. [ROCKNIX website](https://rocknix.org).\n\n"
+                "## On the device { #install }\n")
+        self.assertEqual(
+            gs._page_description(body, Path("platforms/rocknix.md"), "ROCKNIX"),
+            "The BIOS files for ROCKNIX, the folder they go in and the command that installs "
+            "them. A system for handhelds.")
+
     def test_a_console_page_is_described_by_its_start_line(self) -> None:
         body = "# Sega: Dreamcast\n\nPart of Sega.\n\n**Start with**: `dc_boot.bin`, `dc_flash.bin`.\n"
         text = gs._page_description(body, Path("systems/sega-dreamcast.md"), "Sega: Dreamcast")