Fix flake-update pipeline and update ringtail flake inputs

The `--exclude` flag added in #321 never existed in nix — it was
introduced broken and never tested. Replace with dynamic input
discovery: query `nix flake metadata --json` for all input names,
filter out skip_inputs (default: nixpkgs-services), pass the rest
as positional args. Also bump NIX_IMAGE 2.33.3 → 2.34.4.

Updated inputs: nixpkgs, home-manager, disko.
nixpkgs-services stays pinned.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

nixos/ringtail/flake.lock

@@ -27,11 +27,11 @@
         ]
       },
       "locked": {
-        "lastModified": 1774559029,
-        "narHash": "sha256-deix7yg3j6AhjMPnFDCmWB3f83LsajaaULP5HH2j34k=",
+        "lastModified": 1775425411,
+        "narHash": "sha256-KY6HsebJHEe5nHOWP7ur09mb0drGxYSzE3rQxy62rJo=",
         "owner": "nix-community",
         "repo": "home-manager",
-        "rev": "a0bb0d11514f92b639514220114ac8063c72d0a3",
+        "rev": "0d02ec1d0a05f88ef9e74b516842900c41f0f2fe",
         "type": "github"
       },
       "original": {
@@ -43,11 +43,11 @@
     },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1774388614,
-        "narHash": "sha256-tFwzTI0DdDzovdE9+Ras6CUss0yn8P9XV4Ja6RjA+nU=",
+        "lastModified": 1775305101,
+        "narHash": "sha256-/74n1oQPtKG52Yw41cbToxspxHbYz6O3vi+XEw16Qe8=",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "1073dad219cb244572b74da2b20c7fe39cb3fa9e",
+        "rev": "36a601196c4ebf49e035270e10b2d103fe39076b",
         "type": "github"
       },
       "original": {