Remove contributing and component docs from the public docs site

Drop the Contributing and internals section, Architecture, Frontend,
and dp-* component pages from the docs registry, prose files, nav, and
legacy redirect target. Guard with tests that fail if they return.

tests/api/docs/removed_internals.py

@@ -0,0 +1,87 @@
+# retoor <retoor@molodetz.nl>
+import re
+
+from molodetz.docs_prose import DOCS_PAGES, PROSE_DIR, SECTIONS
+
+BANNED_SECTION = "Contributing and internals"
+BANNED_TITLES = {
+    "Architecture",
+    "Frontend and components",
+    "dp-avatar",
+    "dp-code",
+    "dp-content",
+    "dp-title",
+    "dp-toast",
+    "dp-dialog",
+    "dp-context-menu",
+    "dp-upload",
+    "dp-lightbox",
+    "dp-chat",
+}
+BANNED_SLUGS = {
+    "architecture",
+    "frontend",
+    "component-avatar",
+    "component-code",
+    "component-content",
+    "component-title",
+    "component-toast",
+    "component-dialog",
+    "component-context-menu",
+    "component-upload",
+    "component-lightbox",
+    "component-chat",
+}
+BANNED_FILES = {
+    "architecture.md",
+    "frontend.md",
+    *[
+        f"component-{name}.md"
+        for name in (
+            "avatar",
+            "code",
+            "content",
+            "title",
+            "toast",
+            "dialog",
+            "context-menu",
+            "upload",
+            "lightbox",
+            "chat",
+        )
+    ],
+}
+
+
+def _docs_surfaces(html):
+    sidebar = re.search(r'<aside class="docs-sidebar">(.*?)</aside>', html, re.S)
+    content = re.search(r'<article class="docs-content[^"]*">(.*?)</article>', html, re.S)
+    return (sidebar.group(1) if sidebar else ""), (content.group(1) if content else "")
+
+
+def test_docs_registry_excludes_removed_internals():
+    assert BANNED_SECTION not in SECTIONS
+    titles = {page["title"] for page in DOCS_PAGES}
+    slugs = {page["slug"] for page in DOCS_PAGES}
+    sections = {page["section"] for page in DOCS_PAGES}
+    assert not titles & BANNED_TITLES
+    assert not slugs & BANNED_SLUGS
+    assert BANNED_SECTION not in sections
+    for name in BANNED_FILES:
+        assert not (PROSE_DIR / name).exists(), name
+
+
+def test_served_docs_hide_removed_internals(anon, admin):
+    banned_hrefs = {f"/docs/{slug}" for slug in BANNED_SLUGS}
+    for client in (anon, admin):
+        for path in ("/docs", "/docs/welcome", "/docs/api"):
+            html = client.get(path).text
+            sidebar, content = _docs_surfaces(html)
+            surface = f"{sidebar}\n{content}"
+            assert BANNED_SECTION not in surface, path
+            for title in BANNED_TITLES:
+                assert title not in surface, (path, title)
+            for href in banned_hrefs:
+                assert href not in surface, (path, href)
+    for slug in sorted(BANNED_SLUGS):
+        assert anon.get(f"/docs/{slug}").status_code == 404, slug