Generate a _Sidebar page so the wiki shows its subpages

Task: MIL-005#3

tools/build_wiki.py

@@ -184,9 +184,41 @@ def render_page(page: Page, repo_root: Path = REPO_ROOT) -> str:
     return banner + body + "\n"
 
 
+# Link text of the sidebar: English, then one list per translation code.
+SIDEBAR_TITLE = "TirSystem GitHub Actions"
+SIDEBAR_LABELS: dict[str, tuple[str, ...]] = {
+    "en": ("Home", "Onboarding", "Credentials", "Troubleshooting", "Quality checks", "Upgrading", "Capabilities"),
+    "da": ("Hjem", "Tilslutning", "Credentials", "Fejlfinding", "Kvalitetskontrol", "Opgradering", "Kapabiliteter"),
+    "ms": ("Utama", "Menyertakan", "Kelayakan", "Diagnosis", "Semakan kualiti", "Menaik taraf", "Keupayaan"),
+}
+SIDEBAR_NAME = "_Sidebar.md"
+
+
+def render_sidebar() -> str:
+    """Return the navigation shown beside every wiki page.
+
+    Gitea lists subpages only through a ``_Sidebar`` page, so without it a
+    visitor sees the home page and no way to the others.
+    """
+    languages = (("en", "English", ""), *((code, label, f".{code}") for code, label in LANGUAGES))
+    lines = [
+        f"<!-- Generated by {GENERATOR}. Edit the generator, not this page. -->",
+        "",
+        f"**{SIDEBAR_TITLE}**",
+    ]
+    for code, label, suffix in languages:
+        labels = SIDEBAR_LABELS[code]
+        assert len(labels) == len(PAGES), "one sidebar label per page"
+        lines += ["", f"**{label}**", ""]
+        lines += [f"- [{text}]({page.name}{suffix})" for text, page in zip(labels, PAGES)]
+    return chr(10).join(lines) + chr(10)
+
+
 def build_all(repo_root: Path = REPO_ROOT) -> dict[str, str]:
-    """Return ``{file name: content}`` for every English page."""
-    return {f"{page.name}.md": render_page(page, repo_root) for page in PAGES}
+    """Return ``{file name: content}`` for every English page and the sidebar."""
+    pages = {f"{page.name}.md": render_page(page, repo_root) for page in PAGES}
+    pages[SIDEBAR_NAME] = render_sidebar()
+    return pages
 
 
 def write_pages(wiki_dir: Path = WIKI_DIR, repo_root: Path = REPO_ROOT) -> list[str]: