chore(tooling): re-add nix flake and update deps

flake.nix

@@ -0,0 +1,55 @@
+{
+  description = "SeaCogs Nix Flake";
+  inputs.nixpkgs.url = "https://flakehub.com/f/NixOS/nixpkgs/0.1.*.tar.gz";
+
+  outputs =
+    { self, nixpkgs }:
+    let
+      supportedSystems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "aarch64-darwin"
+      ];
+      forEachSupportedSystem =
+        f:
+        nixpkgs.lib.genAttrs supportedSystems (
+          system:
+          f {
+            pkgs = import nixpkgs { inherit system; };
+          }
+        );
+    in
+    {
+      devShells = forEachSupportedSystem (
+        { pkgs }:
+        {
+          default = pkgs.mkShell {
+            packages = with pkgs; [
+              python311
+              uv
+              forgejo-runner
+              # Red-DiscordBot dependencies
+              git
+              libsodium
+              libffi
+              libaio
+              jdk17
+              # Material for MkDocs dependencies
+              cairo
+              pngquant
+            ];
+            shellHook = # bash
+              ''
+                export UV_PYTHON_PREFERENCE=only-system
+                export UV_PYTHON_DOWNLOADS=never
+                uv sync --all-groups
+                alias uvr="uv run"
+                source ./.venv/bin/activate
+                export PYTHONPATH=`pwd`/.venv/${pkgs.python311.sitePackages}/:$PYTHONPATH
+              '';
+          };
+        }
+      );
+    };
+}