fix(ai): codeium not available after auth (#6926)

- Change event from InsertEnter to BufReadPost to load plugin when opening files
  This ensures Codeium is initialized before statusline rendering and provides
  completions immediately when editing a file.

- Improve lualine status component to check if codeium is loaded
  Previously used cmp_source which depends on cmp being loaded and registered.
  Now checks if the codeium module is available, providing better feedback.

Fixes issue where codeium showed no status on statusline and no completions
after successful authentication.

lua/lazyvim/plugins/extras/ai/codeium.lua

@@ -4,7 +4,7 @@ return {
   {
     "Exafunction/codeium.nvim",
     cmd = "Codeium",
-    event = "InsertEnter",
+    event = "BufReadPost",
     build = ":Codeium Auth",
     opts = {
       enable_cmp_source = vim.g.ai_cmp,
@@ -52,7 +52,13 @@ return {
     optional = true,
     event = "VeryLazy",
     opts = function(_, opts)
-      table.insert(opts.sections.lualine_x, 2, LazyVim.lualine.cmp_source("codeium"))
+      table.insert(opts.sections.lualine_x, 2, LazyVim.lualine.status(LazyVim.config.icons.kinds.Codeium, function()
+        local codeium_enabled = package.loaded["codeium"] ~= nil
+        if not codeium_enabled then
+          return
+        end
+        return "ok"
+      end))
     end,
   },