feat: add AJAX batch enrichment (v4.4.0)

Replace the WP-Cron-based re-enrichment with an AJAX polling approach
that processes one peptide per request. This bypasses WP-Cron entirely,
which is unreliable on Hostinger shared hosting with LiteSpeed + Cloudflare.

New files:
- includes/class-psa-batch-enrichment.php — AJAX endpoints for status + process
- assets/js/psa-batch-enrich.js — Admin progress bar UI with polling loop

The admin settings page now shows a "Re-enrich Peptides" button with live
progress bar, per-item log, and automatic retry on failure. Respects the
daily generation cap and monthly budget.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

ARCHITECTURE.md

@@ -27,12 +27,14 @@ peptide-search-ai/
 │   ├── class-psa-cost-tracker.php     API usage logging, monthly budget enforcement, cost estimation
 │   ├── class-psa-pubchem.php          PubChem PUG REST API integration for molecular enrichment
 │   ├── class-psa-admin.php            Settings page, usage dashboard, migration tools, re-enrichment actions
+│   ├── class-psa-batch-enrichment.php AJAX-based batch re-enrichment (processes one peptide per request, no WP-Cron)
 │   └── class-psa-template.php         Single peptide page rendering; quick-facts, extended data, badges
 │
 ├── assets/
 │   ├── js/
 │   │   ├── peptide-search.js          Frontend search, AJAX handler, result rendering (jQuery)
-│   │   └── psa-directory.js           Directory grid, category filters, detail modal (vanilla JS)
+│   │   ├── psa-directory.js           Directory grid, category filters, detail modal (vanilla JS)
+│   │   └── psa-batch-enrich.js       Admin batch enrichment UI (progress bar, AJAX polling loop)
 │   └── css/
 │       ├── peptide-search.css         Scoped styles for search UI, results, pending states, badges
 │       └── psa-directory.css          Directory card grid, filter pills, modal styles, dark mode support