Make the home page's AS name search work (closes #151)

The AS Name Search card on the home page said the search was coming
soon. It now asks the new GET /api/v1/search/as?q=<text>, which
searches the AS list built into asinfo, and lists the matches as links
to their AS pages. An empty q answers 400. asinfo.Search now ignores
case and returns its matches in AS number order.

A match can be an AS that the database does not hold yet. Its AS page
and /api/v1/as/{asn} now answer with its handle and description from
asinfo and no prefixes, instead of 404. Empty prefix lists in that JSON
answer are [] rather than null.

Model: opus-5-5

internal/templates/as_detail.html

@@ -235,7 +235,7 @@
             </div>
             <div class="info-card">
                 <div class="info-label">First Seen</div>
-                <div class="info-value">{{.ASN.FirstSeen.Format "2006-01-02"}}</div>
+                <div class="info-value">{{if .ASN.FirstSeen.IsZero}}Never{{else}}{{.ASN.FirstSeen.Format "2006-01-02"}}{{end}}</div>
             </div>
         </div>