feat(api-keys): restrict keys to source IP addresses

A key can be limited to IP addresses or CIDR networks (e.g. the Wabenhain
server); a stolen key is useless from anywhere else. Requests from other
addresses get 403 "not allowed for this IP" and a log line. The admin UI
asks for the addresses when creating a key, warns when a key works from
anywhere, shows the last source address and can take it over into the
allowlist - changing the list needs no new key (PATCH /api-keys/:id).

Also: a key can only carry scopes its creator holds.

Co-Authored-By: Claude Opus 5.5 (1M context) <[email protected]>

ApiCore-Backend/prisma/migrations/20261001120000_api_key_ip_allowlist/migration.sql

@@ -0,0 +1,3 @@
+-- API keys can be limited to source addresses (IP or CIDR).
+ALTER TABLE "ApiKey" ADD COLUMN "allowedIps" TEXT[] DEFAULT ARRAY[]::TEXT[];
+ALTER TABLE "ApiKey" ADD COLUMN "lastUsedIp" TEXT;