feat: enrich /lookup with university domain list check

Add a second detection path alongside ASN lookup: a self-maintained
list of university domains (uni_domains.txt) loaded at startup.

- New /lookup params: email= (extracts domain from address), domain= unchanged
- Suffix matching: insti.uni-stuttgart.de matches list entry uni-stuttgart.de
  without false-positives (evil-uni-stuttgart.de does not match)
- New response fields: asn_match, domain_match, matched_domain (omitempty)
- nren remains true if either asn_match OR domain_match is true (backwards compat)
- /healthz now returns JSON body: {"asn_count":N,"domain_count":N}
- asn-updater: new update_uni_domains() merges hs-kompass.de TSV + Hipo JSON
  (configurable via UNI_DOMAIN_COUNTRIES / HS_KOMPASS_URL env vars)
- 7 new tests; all existing tests pass unchanged

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

asn-updater/example.env

@@ -17,3 +17,9 @@ HTTP_TIMEOUT=30
 
 # Update interval (seconds, default 30 days)
 INTERVAL_SECONDS=2592000
+
+# Comma-separated ISO country codes for Hipo university domain list filter
+UNI_DOMAIN_COUNTRIES=DE,AT
+
+# Source URL for German university list (hs-kompass.de TSV)
+HS_KOMPASS_URL=https://hs-kompass.de/kompass/xml/download/hs_liste.txt