feat: scaffold Nix flake with dotnet-sdk_9, typst, and nodejs

- devShells.default provides dotnetCorePackages.sdk_9_0, typst, nodejs
- packages.default uses buildDotnetModule with net9.0 target via callPackage
- Stub plugin/ project with minimal .csproj
- .gitignore with .NET/Nix build artifacts

.gitignore

@@ -0,0 +1,14 @@
+# .NET build artifacts
+bin/
+obj/
+*.dll
+
+# Nix
+.result/
+result
+
+# IDE
+.vs/
+.vscode/
+*.user
+*.suo

deps.json

@@ -0,0 +1 @@
+[]

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1778443072,
+        "narHash": "sha256-zi7/fsqM/kFdNuED//4WOCUtezGtKKqRNORjMvfwjnA=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "da5ad661ba4e5ef59ba743f0d112cbc30e474f32",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,72 @@
+{
+  description = "Jellyfin Lessons — a Jellyfin plugin";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+  };
+
+  outputs =
+    { self, nixpkgs }:
+    let
+      forAllSystems =
+        fn: nixpkgs.lib.genAttrs nixpkgs.lib.systems.flakeExposed fn;
+    in
+    {
+      devShells = forAllSystems (
+        system:
+        let
+          pkgs = nixpkgs.legacyPackages.${system};
+        in
+        {
+          default = pkgs.mkShell {
+            packages = [
+              pkgs.dotnetCorePackages.sdk_9_0
+              pkgs.typst
+              pkgs.nodejs
+            ];
+
+            shellHook = ''
+              echo "jellyfin-lessons dev shell"
+              echo "  dotnet: $(dotnet --version)"
+              echo "  typst:  $(typst --version)"
+              echo "  node:   $(node --version)"
+            '';
+          };
+        }
+      );
+
+      packages = forAllSystems (
+        system:
+        let
+          pkgs = nixpkgs.legacyPackages.${system};
+        in
+        {
+          default = pkgs.callPackage (
+            {
+              buildDotnetModule,
+              dotnetCorePackages,
+              lib,
+            }:
+            buildDotnetModule {
+              pname = "jellyfin-lessons";
+              version = "0.1.0";
+
+              src = self;
+
+              projectFile = "plugin/jellyfin-lessons.csproj";
+              nugetDeps = ./deps.json;
+
+              dotnet-sdk = dotnetCorePackages.sdk_9_0;
+              dotnet-runtime = dotnetCorePackages.aspnetcore_9_0;
+
+              meta = {
+                description = "Jellyfin Lessons plugin";
+                license = lib.licenses.mit;
+                platforms = lib.platforms.all;
+              };
+            }
+          ) { };
+        }
+      );
+    };
+}

plugin/jellyfin-lessons.csproj

@@ -0,0 +1,7 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <PropertyGroup>
+    <TargetFramework>net9.0</TargetFramework>
+    <RootNamespace>JellyfinLessons</RootNamespace>
+    <AssemblyName>jellyfin-lessons</AssemblyName>
+  </PropertyGroup>
+</Project>