Manual rebuild hook + polish: single title h1, '›' tree marker

- deploy/rebuild-hook.py: tiny stdlib HTTP service (:18101) — button
  page for the Homepage dashboard iframe, POST /rebuild runs
  auto-build.sh --force, /status + /healthz for feedback/monitoring
- auto-build.sh: --force flag + flock so timer and manual builds
  serialize
- [...slug].astro: skip the synthetic h1 when the note body already
  opens with an identical h1

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/layouts/Base.astro

@@ -455,7 +455,7 @@ const showToc = headings.filter((h) => h.depth <= 3).length >= 2;
         list-style: none;
       }
       .sidebar summary::before {
-        content: '▸';
+        content: '›';
         display: inline-block;
         width: 0.9em;
         color: var(--muted);

src/pages/[...slug].astro

@@ -61,6 +61,11 @@ const title = entry
   : listing.name;
 const rendered = entry ? await render(entry) : null;
 const Content = rendered?.Content ?? null;
+// notes whose body already opens with an identical h1 (common vault
+// pattern) would show a doubled title — skip the synthetic one
+const contentLeadsWithTitle =
+  rendered?.headings?.[0]?.depth === 1 &&
+  rendered.headings[0].text.trim() === String(title).trim();
 ---
 
 <Base
@@ -68,7 +73,7 @@ const Content = rendered?.Content ?? null;
   description={entry?.data.description}
   headings={rendered?.headings ?? []}
 >
-  <h1>{title}</h1>
+  {!contentLeadsWithTitle && <h1>{title}</h1>}
   {Content && <Content />}
   {
     listing && (