Give every view a TSIG key that selects it

Each view's match-clients starts with "key jarl-view-NAME" (after
"!key" for the views listed after it), so a query signed with a view's
key lands in that view from any address. The secrets are derived from a
random seed in Jarl's database. The delegation check signs its queries
to this server's own addresses with the key of the zone's view: before,
they got whichever view matched the server's address, usually internal.
jarl view key / GET /views/{id}/key show a key for dig -k (tsig:write,
audited). jarl-view- key names are reserved; the importer drops view
keys from a configuration Jarl wrote.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/api.md

@@ -386,6 +386,7 @@ Disabling a record that is already disabled is a 409; with `missing_ok=1`
 | GET / PATCH / DELETE | `/views/{id}` | DELETE `?cascade=1` also deletes the view's zones |
 | POST | `/views/order` | `{"ids": [3, 1, 2]}` |
 | PUT | `/views/{id}/color` | `{"color": "green"}`; `""` for the default |
+| GET | `/views/{id}/key` | `{name, algorithm, secret}`: the TSIG key that selects the view (docs/views.md); needs `tsig:write`, audited |
 
 `adopt_zones` moves zones that are not in a view into the new view. named
 requires every zone to be in a view as soon as one view exists.