zen: overhaul configuration

Declaratively configure plugin installation and configuration.

Use my own self-hosted sync server.

flake.lock

@@ -175,6 +175,28 @@
         "type": "github"
       }
     },
+    "firefox-addons": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "dir": "pkgs/firefox-addons",
+        "lastModified": 1774065775,
+        "narHash": "sha256-anJXbdfZMhXWjHSfB5v6e8+yv1ASTHM4TwikH8tloMI=",
+        "owner": "rycee",
+        "repo": "nur-expressions",
+        "rev": "4b3bbb9dc3c80d1b62228c9a2ca0bef74a24a192",
+        "type": "gitlab"
+      },
+      "original": {
+        "dir": "pkgs/firefox-addons",
+        "owner": "rycee",
+        "repo": "nur-expressions",
+        "type": "gitlab"
+      }
+    },
     "flake-compat": {
       "flake": false,
       "locked": {
@@ -695,6 +717,7 @@
         "deploy-rs": "deploy-rs",
         "disko": "disko",
         "emacs-overlay": "emacs-overlay",
+        "firefox-addons": "firefox-addons",
         "home-manager": "home-manager",
         "impermanence": "impermanence",
         "jovian-nixos": "jovian-nixos",