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/validation.md

@@ -71,7 +71,7 @@ showing them.
 | `acl_ref_missing`, `key_ref_missing` | error | Every ACL or TSIG key that is referenced must exist |
 | `acl_cycle` | error | ACLs that include each other |
 | `acl_duplicate`, `acl_name_invalid`, `acl_empty`, `acl_shadowed` | error / warning | Unique names, built-in names reserved, elements that can never match |
-| `key_*` | error / warning | Valid key names, a supported algorithm, a base64 secret of a sensible length. hmac-md5/sha1 are flagged as weak |
+| `key_*` | error / warning | Valid key names, a supported algorithm, a base64 secret of a sensible length. hmac-md5/sha1 are flagged as weak. Names starting with `jarl-view-` are reserved for the view keys (`key_name_reserved`) |
 | `view_duplicate`, `view_name_invalid`, `view_acl_invalid` | error | Valid, unique views and match lists |
 | `view_unreachable` | warning | A view that comes after one matching every client is never used |
 | `option_unknown`, `option_scope_invalid` | error | The option must exist in BIND 9.20 and be allowed where it is set (server, view, zone of this type, top level) |