Extract and store outbound links (backlinks) during content fetch

Adds a backlinks table: one row per <a href> on a captured page that
points at a different domain (same-site nav links are skipped).
Piggybacks on the existing --with-metadata WARC fetch/DOM-parse in
WarcRecordFetcher rather than a separate command/job, since extracting
links needs the same HTML already being downloaded for
title/description/content — no extra requests.

WarcRecordFetcher gains href resolution (absolute, protocol-relative,
root-relative, query-only, and plain relative hrefs) against the
page's own URL. CommonCrawlIndexService::saveBacklinks() replaces a
page's link set wholesale on each (re)fetch, so reruns stay
idempotent. Site gets outboundLinks()/inboundLinks() relations, the
latter keyed by domain string since a link's target site may not be
indexed yet.

Verified against real .es data: 781 backlinks extracted across 205
distinct target domains (social platforms, Trustpilot, genuine
inter-site links with correct anchor text), and a rerun of the same
fetch left the count unchanged.

app/Services/CommonCrawl/CommonCrawlIndexService.php

@@ -2,6 +2,7 @@
 
 namespace App\Services\CommonCrawl;
 
+use App\Models\Backlink;
 use App\Models\Site;
 use App\Models\SitePage;
 use App\Support\CommonCrawl\WarcRecordFetcher;
@@ -138,8 +139,13 @@ class CommonCrawlIndexService
             unset($attributes['collection'], $attributes['domain']);
             $attributes['urlkey_hash'] = sha1($page['urlkey']);
 
+            $links = [];
+
             if ($withContent) {
-                $attributes = array_merge($attributes, $this->fetchContent($page, $contentCache));
+                $content = $this->fetchContent($page, $contentCache);
+                $links = $content['links'] ?? [];
+                unset($content['links']);
+                $attributes = array_merge($attributes, $content);
             }
 
             $result = SitePage::updateOrCreate(
@@ -148,6 +154,10 @@ class CommonCrawlIndexService
             );
 
             $result->wasRecentlyCreated ? $pagesCreated++ : $pagesUpdated++;
+
+            if ($withContent) {
+                $this->saveBacklinks($result, $site, $links);
+            }
         }
 
         return [
@@ -158,6 +168,40 @@ class CommonCrawlIndexService
         ];
     }
 
+    /**
+     * Replace a page's recorded outbound links wholesale — simpler and more correct
+     * than diffing against what was there before, since a page's actual link set can
+     * change between crawls.
+     */
+    private function saveBacklinks(SitePage $sitePage, Site $site, array $links): void
+    {
+        $sitePage->links()->delete();
+
+        if (empty($links)) {
+            return;
+        }
+
+        $now = now();
+
+        $rows = collect($links)
+            ->unique('url')
+            ->map(fn (array $link) => [
+                'site_id' => $site->id,
+                'site_page_id' => $sitePage->id,
+                'target_url' => $link['url'],
+                'target_url_hash' => sha1($link['url']),
+                'target_domain' => $link['domain'],
+                'anchor_text' => $link['anchor_text'],
+                'rel' => $link['rel'],
+                'created_at' => $now,
+                'updated_at' => $now,
+            ])
+            ->values()
+            ->all();
+
+        Backlink::insert($rows);
+    }
+
     /**
      * List every CDX shard file for a collection, straight from the bulk data storage
      * (data.commoncrawl.org) rather than the index.commoncrawl.org query API — this is