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> and lists the matches
as links to their AS pages. asinfo.Search ignores case, returns the first
matches up to a limit in AS number order, and counts all matches. An
empty q answers 400.

When the database has no record of an AS, its page and /api/v1/as/{asn}
take its handle and description from asinfo and still list its prefixes.
They answer 404 only for an AS with no record, no asinfo entry and no
prefix. AS 0 means no known origin: it always answers 404, and the search
never lists it.

Model: opus-5-5

README.md

@@ -56,15 +56,17 @@ 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
   database answers and the RIS Live feed is connected, otherwise 503;
   `data.status` is `ok` or `error` and `data.checks` says which check failed
 - `GET /as/{asn}` - AS detail page (HTML): the prefixes the AS originates and
-  its peers
+  its peers. When the database has no record of the AS, its handle and
+  description come from the AS list built into RouteWatch. The page then shows
+  no first-seen date.
 - `GET /prefix/{prefix}/{length}` - Prefix detail page (HTML), such as
   `/prefix/192.0.2.0/24`: every live route for the prefix, one per peer, and its
   origin ASes
@@ -93,9 +95,22 @@ Every route answers `HEAD` as it answers `GET`, without the body.
   and 404 when none of the addresses has a live route. A PTR lookup gets 2
   seconds; an address whose lookup takes longer is answered without PTR names.
 - `GET /api/v1/as/{asn}` - The AS and the prefixes it originates, IPv4 and IPv6
-  apart, each with when its newest route was updated
+  apart, each with when its newest route was updated. When the database has no
+  record of the AS, its handle and description come from the AS list built into
+  RouteWatch. The answer then has no `first_seen` or `last_seen`.
 - `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, not the database. The
+    list comes from [ipverse/asn-info](https://github.com/ipverse/asn-info). A
+    match can therefore be an AS that the database has no record of. 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
@@ -106,13 +121,16 @@ took. The health check is the exception: its 503 answer is also
 A request that runs past its time limit answers 504: the limit is 30 seconds,
 and 4 seconds for the database reads behind `/status.json` and `/api/v1/stats`.
 An AS number, prefix or mask length that does not parse answers 400, as does a
-mask length out of range for its IP version. An AS the database does not hold,
-or a prefix with no live route, answers 404. The HTML pages give these errors as
-plain text. Under `/api/v1` and `/ip/`, a path no route matches answers 404 with
-the message `Not found`, and `POST`, `PUT`, `PATCH`, `DELETE`, `OPTIONS`,
-`TRACE` or `CONNECT` answers 405 with `Method not allowed`. A 500 answer says
-only `Internal server error`, and a host name that does not resolve only
-`could not resolve host name`; the detail goes to the log.
+mask length out of range for its IP version. An AS answers 404 when it is not in
+the AS list built into RouteWatch and the database has neither a record of it
+nor a live route it originates. AS 0 always answers 404, because it means no
+known origin. The AS name search never lists it. A prefix with no live route
+answers 404 too. The HTML pages give these errors as plain text. Under `/api/v1`
+and `/ip/`, a path no route matches answers 404 with the message `Not found`,
+and `POST`, `PUT`, `PATCH`, `DELETE`, `OPTIONS`, `TRACE` or `CONNECT` answers
+405 with `Method not allowed`. A 500 answer says only `Internal server error`,
+and a host name that does not resolve only `could not resolve host name`; the
+detail goes to the log.
 
 Every answer carries `Strict-Transport-Security`, `Content-Security-Policy`,
 `X-Frame-Options`, `X-Content-Type-Options`, `Referrer-Policy` and