fix(core): extract HTML title after font stripping, not before

SingleFile embeds fonts as base64 data URIs in <style> blocks in the
<head>, pushing the <title> tag to ~1.2 MB in the raw temp file.
The 256 KiB read window in extract_html_title missed it.

Font extraction rewrites the HTML in-place (2.4 MB → 1.26 MB) before
hashing, so the title is accessible at byte ~106 KB in that content.

Fix: add extract_html_title_str() that operates on a &str; call it on
the in-memory rewritten string after font extraction (server path).
CLI path (no font extraction) falls back to result.title as before.

crates/archivr-core/src/downloader/singlefile.rs

@@ -691,7 +691,20 @@ fn extract_html_title(path: &Path) -> Option<String> {
     let mut f = std::fs::File::open(path).ok()?;
     let mut buf = Vec::new();
     f.take(256 * 1024).read_to_end(&mut buf).ok()?;
-    let lower = String::from_utf8_lossy(&buf).to_ascii_lowercase();
+    extract_html_title_from_buf(&buf)
+}
+
+/// Extracts the `<title>` content from an HTML string.
+///
+/// Used in the server capture path where the font-extracted HTML is already
+/// in memory — avoids a re-read and operates on the smaller post-extraction
+/// content where the title is guaranteed to be within range.
+pub fn extract_html_title_str(html: &str) -> Option<String> {
+    extract_html_title_from_buf(html.as_bytes())
+}
+
+fn extract_html_title_from_buf(buf: &[u8]) -> Option<String> {
+    let lower = String::from_utf8_lossy(buf).to_ascii_lowercase();
     let start = lower.find("<title>")? + "<title>".len();
     let end = lower[start..].find("</title>")? + start;
     let title = String::from_utf8_lossy(&buf[start..end])