Merge feat/remote-builders into uconsole-cm5-incremental

Bidirectional remote building + rename uconsole-cm5 -> uConsole:
- Rename all uconsole-cm5 refs to uConsole (nixosSystem key, paths, module)
- Replace single-machine remote-builder module with multi-machine config
- Enable remote builder on lazyworkhorse -> uConsole (aarch64)
- Enable remote builder on uConsole -> lazyworkhorse (x86_64)
- Add builder system user + SSH key via agenix-rekey (secrets/builder_key.age)
- Add builder_key + gortium_password age secrets to all hosts
- Fix pre-existing bugs: missing modules in lazyworkhorse/cyt-pi,
  SSH config structure (hostKeys outside settings), cyt-pi inline user
- Remove obsolete openclaw-node service + module + age secrets

secrets/openclaw_gateway_token.age

@@ -1,11 +0,0 @@
------BEGIN AGE ENCRYPTED FILE-----
-YWdlLWVuY3J5cHRpb24ub3JnL3YxCi0+IHNzaC1lZDI1NTE5IEdoTUQ4QSBCWEpO
-cG9yNnFpcHFqTkNzTngxU1MxN0NYK0hrZFhUTjVORWFrK3JNd2tZCmtMTGpwQk1E
-WlUwL3N6SGRWblpnNEkrWkkyU2hQMkRIK0M3R0pOVEREV3MKLT4gY2osLWdyZWFz
-ZSBacSozVVQgUCAxRS1OQSAuKXxDPCoKbStWNW1BZjBZQzNDaTlDbU5EZkxsRWxM
-cXJ3dDU1RDNpOXRlV0tzdEp2NUo3S1lhRG5Md0RHTGlJdkFSYmt5YQo4R1hiQWRG
-V2VxekJKZwotLS0geG1XSi9VbkhXZHQzcEFVS3hKNzVueXFLa2xnZTc3Q2tJTVZ5
-eXJabWk5Ywp6bJCP3s0xxzjE+eTR+cv7ZUnkoliT/n7uIprq1BTn/LIRLkUTUqs3
-NiDwrXcoq4/QKd0Dt+8ap3vFAuusjGxRlnYMaRrZie2AGtTV8U7Q7durm9o2K+/4
-QzRQ/MtumIQm
------END AGE ENCRYPTED FILE-----

secrets/secrets.nix

@@ -12,5 +12,5 @@ in
   "home_wifi.age".publicKeys = authorizedKeys;
   "lazyworkhorse_host_ssh_key.age".publicKeys = authorizedKeys;
   "n8n_ssh_key.age".publicKeys = authorizedKeys;
-  "openclaw_gateway_token.age".publicKeys = authorizedKeys;
+  "builder_key.age".publicKeys = authorizedKeys;
 }