docs: title the migration page with its H1, and move the posthog.com SDK page into the reference

bin/docs_scripts/generate_markdown.py

@@ -214,6 +214,16 @@ def nest(markdown: str) -> str:
     return "\n".join(out)
 
 
+def migration_page(guides: list[str]) -> list[str]:
+    """The migration page. One guide's H1 becomes the page title, so the page shows one title."""
+    title = "PostHog Python SDK migration guides"
+    if len(guides) == 1 and guides[0].startswith("# "):
+        heading, _, rest = guides[0].partition("\n")
+        title, guides = heading[2:].strip(), [rest.strip()]
+    head = f"---\ntitle: {json.dumps(title)}\nsidebar: Docs\nshowTitle: true\n---"
+    return [head, *guides]
+
+
 def write(name: str, sections: list[str]) -> None:
     (ROOT / "references" / name).write_text("\n\n".join(sections) + "\n")
     print(f"wrote references/{name}")
@@ -255,10 +265,9 @@ def main() -> None:
             [front_matter("PostHog Python SDK", body), *body],
         )
     if guides := sorted((ROOT / "docs").glob("migration-*.md"), reverse=True):
-        head = "---\ntitle: PostHog Python SDK migration guides\nsidebar: Docs\nshowTitle: true\n---"
         write(
             "posthog-python-migration.md",
-            [head, *(g.read_text().strip() for g in guides)],
+            migration_page([g.read_text().strip() for g in guides]),
         )