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. The answer holds the query, the number of matches
and the first 50 of them; an empty q answers 400. asinfo.Search now
ignores case, uses strings.Contains instead of its own substring loop,
and returns its matches in AS number order. A number, or AS and a
number, typed into the card still opens that AS's page. The card builds
the list with textContent, since the names come from outside data.

Model: opus-5-5

README.md

@@ -56,8 +56,8 @@ Every route answers `HEAD` as it answers `GET`, without the body.
 
 ### Web Interface
 
-- `GET /` - Home page (HTML): headline figures, and lookups by AS number and by
-  IP address
+- `GET /` - Home page (HTML): headline figures, lookups by AS number and by IP
+  address, and a search of AS names
 - `GET /status` - HTML status dashboard, which reads `/api/v1/stats`
 - `GET /status.json` - JSON statistics: feed, memory, database and route figures
 - `GET /.well-known/healthcheck.json` - Health check (JSON): 200 when the
@@ -96,6 +96,18 @@ Every route answers `HEAD` as it answers `GET`, without the body.
   apart, each with when its newest route was updated
 - `GET /api/v1/prefix/{prefix}/{length}` - Every live route for the prefix, one
   per peer, and the same routes grouped by origin AS in `origins`
+- `GET /api/v1/search/as?q={text}` - Finds the ASes whose handle or description
+  contains `{text}`, ignoring case. `data` holds:
+    - `query`: `{text}` without its leading and trailing spaces
+    - `total`: the number of ASes that match
+    - `results`: the first 50 of them in AS number order, each with `asn`,
+      `handle` and `description`
+
+    The search reads the AS list built into RouteWatch, taken from
+    [ipverse/asn-info](https://github.com/ipverse/asn-info), not the database. A
+    match can therefore be an AS that the database does not hold. Its
+    `/as/{asn}` and `/api/v1/as/{asn}` then answer 404. A `q` that is missing,
+    empty or only spaces answers 400.
 
 A JSON answer is `{"status": "ok", "data": ...}`, or for an error
 `{"status": "error", "error": {"msg": ..., "code": ...}}`, and carries an