feat: add wallpaper renaming tool and nix development environment

Implement a Python script that uses a local vision model (via Ollama) to
automatically rename image files to descriptive snake_case names.

- Add `rename-wallpapers.py` to handle image processing, resizing with
  ffmpeg, and querying the Ollama API.
- Add `flake.nix` to provide a reproducible development environment
  including Python, Ollama, ffmpeg, and other necessary dependencies.

flake.nix

@@ -0,0 +1,45 @@
+{
+  description = "Wallpaper renamer: auto-rename images to descriptive snake_case names using a local vision model (Ollama + llava).";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-25.05";
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+
+        # The rename command. It starts an Ollama server (if needed) and pulls the
+        # vision model on first run, so everything lives inside this shell.
+        rename-wallpapers = pkgs.writeScriptBin "rename-wallpapers"
+          (builtins.readFile ./rename-wallpapers.py);
+      in
+      {
+        packages.default = rename-wallpapers;
+
+        devShells.default = pkgs.mkShell {
+          name = "wallpaper-renamer";
+          packages = [
+            pkgs.ollama
+            pkgs.python3
+            pkgs.curl
+            pkgs.ffmpeg
+            pkgs.fzf
+            pkgs.chafa
+            rename-wallpapers
+          ];
+
+          shellHook = ''
+            echo "wallpaper-renamer shell ready."
+            echo "Usage examples:"
+            echo "  rename-wallpapers                 # rename all images in this dir"
+            echo "  rename-wallpapers --pick          # interactively choose with fzf"
+            echo "  rename-wallpapers --dir ~/Pics    # scan another directory"
+            echo "  rename-wallpapers --dry-run *.jpg # preview without renaming"
+            echo "Model is pulled on first run (one-time download)."
+          '';
+        };
+      });
+}