Use API key from environment if that exists

plugin/gemini/api.lua

@@ -2,12 +2,28 @@
 
 local M = {}
 
-local api_key = vim.g.gemini_api_key -- Get API key from global variable
+local function get_api_key()
+	-- Check for environment variable
+	local api_key = os.getenv("GEMINI_API_KEY")
+	if api_key then
+		return api_key
+	end
+
+	-- Check for Neovim global variable
+	api_key = vim.g.gemini_api_key
+	if api_key then
+		return api_key
+	end
+
+	return nil -- API key not found
+end
 
 local function make_request(prompt)
+	local api_key = get_api_key() -- Get API key from environment or global variable
+
 	if not api_key then
 		vim.notify(
-			"Google AI API key not set.  Set g.gemini_api_key in your init.vim or init.lua.",
+			"Google AI API key not set. Set GEMINI_API_KEY environment variable or g.gemini_api_key in your init.vim or init.lua.",
 			vim.log.levels.ERROR
 		)
 		return nil