feat(prospecting): add content scraping for POC builder (Workstream 3A)

- New scrape_content() method in enrichment_service: extracts meta
  description, H1/H2 headings, paragraphs, images (filtered for size),
  social links, service items, and detected languages using BeautifulSoup
- Scans 6 pages per prospect: /, /about, /a-propos, /services,
  /nos-services, /contact
- Results stored as JSON in prospect.scraped_content_json
- New endpoints: POST /content-scrape/{id} and /content-scrape/batch
- Added to full_enrichment pipeline (Step 5, before security audit)
- CONTENT_SCRAPE job type for scan-jobs tracking
- "Content Scrape" batch button on scan-jobs page
- Add beautifulsoup4 to requirements.txt

Tested on batirenovation-strasbourg.fr: extracted 30 headings,
21 paragraphs, 13 images.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

app/modules/prospecting/templates/prospecting/admin/scan-jobs.html

@@ -34,6 +34,11 @@
             <span x-html="$icon('mail', 'w-4 h-4 mr-2')"></span>
             Contact Scrape
         </button>
+        <button type="button" @click="startBatchJob('content_scrape')"
+                class="inline-flex items-center px-4 py-2 text-sm font-medium leading-5 text-white transition-colors duration-150 bg-teal-600 border border-transparent rounded-lg hover:bg-teal-700 focus:outline-none">
+            <span x-html="$icon('document-text', 'w-4 h-4 mr-2')"></span>
+            Content Scrape
+        </button>
         <button type="button" @click="startBatchJob('security_audit')"
                 class="inline-flex items-center px-4 py-2 text-sm font-medium leading-5 text-white transition-colors duration-150 bg-yellow-600 border border-transparent rounded-lg hover:bg-yellow-700 focus:outline-none">
             <span x-html="$icon('shield-check', 'w-4 h-4 mr-2')"></span>