perf: hot-path extraction speedups (selector hoist, shared og, QuickJS gating)

Rescued from the stale perf/audit-fixes branch — the *perf-only* subset of
that branch's big mixed commit, ported cleanly onto current main with
byte-identical extraction output.

- markdown: hoist the `img[alt]` / `a[href]` selectors out of the per-node
  noise path into `Lazy` statics (stop recompiling them per element).
- extractors: single shared `og()` / `parse_og()` module replaces the
  per-field Open Graph re-scan duplicated across 7 vertical extractors
  (amazon, ebay, ecommerce, etsy, substack, trustpilot, youtube). Each
  vertical now does one pass. Raw-vs-unescaped behaviour preserved exactly.
- core: gate the QuickJS VM on a cheap marker check (skip it entirely when
  the page has no JS-assigned data) and reuse the already-parsed document
  instead of re-parsing the HTML.
- fetch: connection-pool tuning on the wreq client (connect_timeout, idle
  pool, max-idle-per-host, tcp keepalive) for connection reuse.

Output-equivalence is covered by existing tests (amazon quot-entity,
trustpilot title parse, ecommerce/youtube/etsy/substack og fallbacks) — all
green. No new dependencies; no public API change.

Deliberately EXCLUDED from this slice (separate concerns bundled in the
original commit): the `#[non_exhaustive]` API-breaking changes, the LLM/PDF/
server reliability hardening (much already shipped in 0.6.8), the tooling
(cargo-deny, release profile, MSRV), and the retry-loop dedup refactor (a
code-cleanup with no runtime benefit — not worth churning client.rs for).

Original work by the prior author on perf/audit-fixes; this re-applies only
the performance subset onto main.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

crates/webclaw-fetch/src/extractors/substack_post.rs

@@ -28,6 +28,7 @@ use serde::Deserialize;
 use serde_json::{Value, json};
 
 use super::ExtractorInfo;
+use super::og::parse_og;
 use crate::cloud::{self, CloudError};
 use crate::error::FetchError;
 use crate::fetcher::Fetcher;
@@ -181,24 +182,27 @@ async fn html_fallback(
 pub fn parse_html(html: &str, url: &str, api_url: &str, slug: &str) -> Value {
     let article = find_article_jsonld(html);
 
+    // Single scan for the four og:* fields read as fallbacks below.
+    let og_meta = parse_og(html);
+
     let title = article
         .as_ref()
         .and_then(|v| get_text(v, "headline"))
-        .or_else(|| og(html, "title"));
+        .or_else(|| og_meta.raw("title"));
     let description = article
         .as_ref()
         .and_then(|v| get_text(v, "description"))
-        .or_else(|| og(html, "description"));
+        .or_else(|| og_meta.raw("description"));
     let cover_image = article
         .as_ref()
         .and_then(get_first_image)
-        .or_else(|| og(html, "image"));
+        .or_else(|| og_meta.raw("image"));
     let post_date = article
         .as_ref()
         .and_then(|v| get_text(v, "datePublished"))
         .or_else(|| meta_property(html, "article:published_time"));
     let updated_at = article.as_ref().and_then(|v| get_text(v, "dateModified"));
-    let publication_name = og(html, "site_name");
+    let publication_name = og_meta.raw("site_name");
     let authors = article.as_ref().map(extract_authors).unwrap_or_default();
 
     json!({
@@ -302,19 +306,6 @@ fn handle_from_author_url(u: &str) -> Option<String> {
 // HTML tag helpers
 // ---------------------------------------------------------------------------
 
-fn og(html: &str, prop: &str) -> Option<String> {
-    static RE: OnceLock<Regex> = OnceLock::new();
-    let re = RE.get_or_init(|| {
-        Regex::new(r#"(?i)<meta[^>]+property="og:([a-z_]+)"[^>]+content="([^"]+)""#).unwrap()
-    });
-    for c in re.captures_iter(html) {
-        if c.get(1).is_some_and(|m| m.as_str() == prop) {
-            return c.get(2).map(|m| m.as_str().to_string());
-        }
-    }
-    None
-}
-
 /// Pull `<meta property="article:published_time" content="...">` and
 /// similar structured meta tags.
 fn meta_property(html: &str, prop: &str) -> Option<String> {