feat(nix): migrate oatmeal

Using it as homebrew tap instead of Nix
(https://github.com/dustinblackman/oatmeal?tab=readme-ov-file#nix),
because I'm unable to install the NUR repository successfully 🙄

nix/home/default.nix

@@ -17,6 +17,7 @@ in
     ./lazydocker
     ./lazygit
     ./lf
+    ./oatmeal
     ./ripgrep
     ./ruby
     ./skhd

nix/home/oatmeal/config.toml

@@ -0,0 +1,32 @@
+# The initial backend hosting a model to connect to. [possible values: langchain, ollama, openai]
+backend = "ollama"
+
+# Time to wait in milliseconds before timing out when doing a healthcheck for a backend.
+backend-health-check-timeout = 1000
+
+# The editor to integrate with. [possible values: neovim, clipboard, none]
+editor = "neovim"
+
+# The initial model on a backend to consume. Defaults to the first model available from the backend if not set.
+model = "codellama:latest"
+
+# LangChain Serve API URL when using the LangChain backend.
+lang-chain-url = "http://localhost:8000"
+
+# Ollama API URL when using the Ollama backend.
+ollama-url = "http://localhost:11434"
+
+# OpenAI API token when using the OpenAI backend.
+# open-ai-token = ""
+
+# OpenAI API URL when using the OpenAI backend. Can be swapped to a compatible proxy.
+open-ai-url = "https://api.openai.com"
+
+# Sets code syntax highlighting theme. [possible values: base16-github, base16-monokai, base16-one-light, base16-onedark, base16-seti]
+theme = "base16-onedark"
+
+# Absolute path to a TextMate tmTheme to use for code syntax highlighting.
+# theme-file = ""
+
+# Your user name displayed in all chat bubbles.
+# username = ""

nix/home/oatmeal/default.nix

@@ -0,0 +1,7 @@
+{ ... }:
+
+{
+  home.file.".config/oatmeal/config.toml" = {
+    source = ./config.toml;
+  };
+}