feat: add nix flake with fenix rust toolchain

Configure hermetic development environment:

- fenix toolchain from rust-toolchain.toml
- clangStdenv for Tree-sitter C grammar compilation
- Multi-platform devShells (x86_64/aarch64, linux/darwin)
- Generated flake.lock with pinned inputs

.envrc

@@ -0,0 +1 @@
+use flake

.gitignore

@@ -3,4 +3,5 @@ target
 
 # Local Netlify folder
 .netlify
+.direnv
 target/

flake.lock

@@ -0,0 +1,66 @@
+{
+  "nodes": {
+    "fenix": {
+      "inputs": {
+        "nixpkgs": [
+          "nixpkgs"
+        ],
+        "rust-analyzer-src": "rust-analyzer-src"
+      },
+      "locked": {
+        "lastModified": 1769237067,
+        "narHash": "sha256-o2UfbFRcL/UClXaDI8NR3WAulOoda55rdw0oVXAst0A=",
+        "owner": "nix-community",
+        "repo": "fenix",
+        "rev": "93523fa073f781d3d02d326cdbb85f8709b00c40",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-community",
+        "repo": "fenix",
+        "type": "github"
+      }
+    },
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1769268028,
+        "narHash": "sha256-mAdJpV0e5IGZjnE4f/8uf0E4hQR7ptRP00gnZKUOdMo=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "ab9fbbcf4858bd6d40ba2bbec37ceb4ab6e1f562",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "fenix": "fenix",
+        "nixpkgs": "nixpkgs"
+      }
+    },
+    "rust-analyzer-src": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1769166439,
+        "narHash": "sha256-HjSoNRYe8tPdzfhJ0IBQrrJATOrtVKOHvk8OoTew1Do=",
+        "owner": "rust-lang",
+        "repo": "rust-analyzer",
+        "rev": "39018acf3477a26f4e6d2ead6a48954d623adcaa",
+        "type": "github"
+      },
+      "original": {
+        "owner": "rust-lang",
+        "ref": "nightly",
+        "repo": "rust-analyzer",
+        "type": "github"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}

flake.nix

@@ -0,0 +1,52 @@
+{
+  description = "nrd.sh - bespoke static site compiler";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
+    fenix = {
+      url = "github:nix-community/fenix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      fenix,
+    }:
+    let
+      systems = [
+        "x86_64-linux"
+        "aarch64-linux"
+        "x86_64-darwin"
+        "aarch64-darwin"
+      ];
+      forAllSystems = fn: nixpkgs.lib.genAttrs systems (system: fn system);
+    in
+    {
+      devShells = forAllSystems (
+        system:
+        let
+          pkgs = nixpkgs.legacyPackages.${system};
+          fenixPkgs = fenix.packages.${system};
+          toolchain = fenixPkgs.fromToolchainFile { file = ./rust-toolchain.toml; sha256 = "sha256-vra6TkHITpwRyA5oBKAHSX0Mi6CBDNQD+ryPSpxFsfg=";};
+        in
+        {
+          default = pkgs.mkShell.override { stdenv = pkgs.clangStdenv; } {
+            RUST_SRC_PATH = "${toolchain}/lib/rustlib/src/rust/library";
+            packages =
+              [
+                toolchain
+                fenixPkgs.default.rustfmt
+                pkgs.pkg-config
+              ]
+              ++ pkgs.lib.optionals pkgs.stdenv.isDarwin [
+                pkgs.apple-sdk
+                pkgs.libiconv
+              ];
+          };
+        }
+      );
+    };
+}