Use the panel from its own flake (reudy-net/panel)

The panel's code moved to git.reudy.net/reudy-net/panel, which provides a
package and a NixOS module. This config now pulls it in as the `panel`
flake input and only sets services.reudy-panel options, so panel updates
are `nix flake update panel` instead of edits in this repo.

The input uses ssh because the reudy-net org is not visible anonymously.
The generated service, directories, Caddy vhost, routes import and reload
units are unchanged apart from store paths.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01UbWSNkXxZhYf7eqHTyx3Bf

flake.lock

@@ -149,10 +149,32 @@
         "type": "github"
       }
     },
+    "panel": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1790531515,
+        "narHash": "sha256-EeanYOcMIrPGgJt3azJIFjdttHRU07jVY0Iw4awEdpg=",
+        "ref": "main",
+        "rev": "e11fc00840f2fe68a076ea56305ca67bd2ace332",
+        "revCount": 39,
+        "type": "git",
+        "url": "ssh://git@git.reudy.net:14922/reudy-net/panel"
+      },
+      "original": {
+        "ref": "main",
+        "type": "git",
+        "url": "ssh://git@git.reudy.net:14922/reudy-net/panel"
+      }
+    },
     "root": {
       "inputs": {
         "agenix": "agenix",
         "nixpkgs": "nixpkgs",
+        "panel": "panel",
         "vpsadminos": "vpsadminos"
       }
     },