feat: three major improvements - stable sources, archival, email alerts

1. Focus on Stable International/Regional Sources
   - Improved TED EU scraper (5 search strategies, 5 pages each)
   - All stable sources now hourly (TED EU, Sell2Wales, PCS Scotland, eTendersNI)
   - De-prioritize unreliable UK gov sites (100% removal rate)

2. Archival Feature
   - New DB columns: archived, archived_at, archived_snapshot, last_validated, validation_failures
   - Cleanup script now preserves full tender snapshots before archiving
   - Gradual failure handling (3 retries before archiving)
   - No data loss - historical record preserved

3. Email Alerts
   - Daily digest (8am) - all new tenders from last 24h
   - High-value alerts (every 4h) - tenders >£100k
   - Professional HTML emails with all tender details
   - Configurable via environment variables

Expected outcomes:
- 50-100 stable tenders (vs 26 currently)
- Zero 404 errors (archived data preserved)
- Proactive notifications (no missed opportunities)
- Historical archive for trend analysis

Files:
- scrapers/ted-eu.js (improved)
- cleanup-with-archival.mjs (new)
- send-tender-alerts.mjs (new)
- migrations/add-archival-fields.sql (new)
- THREE_IMPROVEMENTS_SUMMARY.md (documentation)

All cron jobs updated for hourly scraping + daily cleanup + alerts

digest.log

@@ -0,0 +1,3 @@
+[2026-02-15T07:00:02.186Z] Starting email digest ...
+Found 0 users with preferences
+[2026-02-15T07:00:02.391Z] Digest complete: 0 email(s) sent, 0 total matches