api/v1: add code-first Huma implementation of the v1 API

Reimplement the v1 API as a code-first Huma service in hscontrol/api/v1,
a thin adapter over the state layer. Huma emits the OpenAPI 3.1 document
(openapi/v1/headscale.yaml) from the Go operation and type definitions;
cmd/gen-openapi writes it and the 3.0.3 downgrade the client is generated
from. Responses reproduce the protojson wire contract (string-encoded
64-bit IDs, all fields emitted, RFC3339/null timestamps); errors map to
the correct HTTP status (404/400/409, 500 for server faults) via mapError.

Serve it on the chi router at /api/v1 behind the existing API-key
middleware, and point /swagger at the emitted spec.

flakehashes.json

@@ -1,6 +1,6 @@
 {
   "vendor": {
-    "goModSum": "sha256-csVm5v6HZ49PBp/FCX+yK1sjV8/nuUQz3GKN21Ne1mg=",
-    "sri": "sha256-fzKyXNMw/2yAEhaTZu0n1NXatPO2IP0HFA2ey1vZIYM="
+    "goModSum": "sha256-tboE8Nc56tKKOki0JVvR64HcTZJE3ESgLnfdOYQq53Q=",
+    "sri": "sha256-82WhhyBCnwp0ysrI+n2vHf22cgD29Pjus3GtIOpJonU="
   }
 }