fix(crawler): wait for page marker instead of fixed 1s sleep (0.36.2)

A chromium snapshot taken between the wrapper-render and row-render
phases let parse_chapter_list return Ok(vec![]) for a manga that
actually has chapters — the soft-drop branch in sync_manga_chapters
then flipped every existing chapter to dropped_at.

Add wait_for_selector to crawler::nav. navigate() now takes a CSS
marker matching the most-specific element the downstream parser will
look for (one of LIST_PAGE_MARKER / DETAIL_PAGE_CHAPTERS_MARKER /
DETAIL_PAGE_LAYOUT_MARKER). The wait is best-effort and capped by
SELECTOR_TIMEOUT (10s); a legitimately empty page can still pass
through because the parser's #chapter_table sentinel and the
universal broken-page body check stay in force.

Same pattern wired at the reader nav (a#pic_container) and probe
nav (#logo), replacing the implicit assumption that the post-load
JS had finished within 1 second.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/src/crawler/session.rs

@@ -206,6 +206,15 @@ async fn fetch_probe_html(browser: &Browser, probe_url: &str) -> anyhow::Result<
     crate::crawler::nav::wait_for_nav(&page)
         .await
         .context("wait for nav on probe")?;
+    // Best-effort wait for the layout marker. Timeout is fine — the
+    // probe classifier handles a missing `#logo` as Transient anyway,
+    // and the verify loop retries on Transient.
+    let _ = crate::crawler::nav::wait_for_selector(
+        &page,
+        "#logo",
+        crate::crawler::nav::SELECTOR_TIMEOUT,
+    )
+    .await;
     let html = page.content().await.context("read probe html")?;
     page.close().await.ok();
     Ok(html)