fix(setup): set language state before setup_code hook on first open

Problem: when opening a contest for the first time (metadata not
cached), the setup_code hook fired before state.set_language() was
called, causing state.get_language() to return nil inside the hook.

Solution: call state.set_language(lang) before the hook in the
provisional-buffer branch of setup_contest(). The value is already
computed at that point and is identical to what setup_problem() sets
later, so the early write is idempotent.

doc/cp.nvim.txt

@@ -205,9 +205,9 @@ Debug Builds ~
 ==============================================================================
 CONFIGURATION                                                      *cp-config*
 
-Configuration is done via `vim.g.cp_config`. Set this before using the plugin:
+Configuration is done via `vim.g.cp`. Set this before using the plugin:
 >lua
-    vim.g.cp_config = {
+    vim.g.cp = {
       languages = {
         cpp = {
           extension = 'cc',
@@ -274,7 +274,7 @@ the default; per-platform overrides can tweak 'extension' or 'commands'.
 
 For example, to run CodeForces contests with Python by default:
 >lua
-    vim.g.cp_config = {
+    vim.g.cp = {
       platforms = {
         codeforces = {
           default_language  = 'python',
@@ -285,7 +285,7 @@ For example, to run CodeForces contests with Python by default:
 Any language is supported provided the proper configuration. For example, to
 run CSES problems with Rust using the single schema:
 >lua
-    vim.g.cp_config = {
+    vim.g.cp = {
       languages = {
         rust = {
           extension = 'rs',

lua/cp/init.lua

@@ -17,7 +17,11 @@ local function ensure_initialized()
   if initialized then
     return
   end
-  local user_config = vim.g.cp_config or {}
+  if vim.g.cp_config then
+    vim.deprecate('vim.g.cp_config', 'vim.g.cp', 'v0.7.6', 'cp.nvim', false)
+    vim.g.cp = vim.g.cp or vim.g.cp_config
+  end
+  local user_config = vim.g.cp or {}
   local config = config_module.setup(user_config)
   config_module.set_current_config(config)
   initialized = true
@@ -34,4 +38,13 @@ function M.is_initialized()
   return initialized
 end
 
+---@deprecated Use `vim.g.cp` instead
+function M.setup(user_config)
+  vim.deprecate('require("cp").setup()', 'vim.g.cp', 'v0.1.0', 'cp.nvim', false)
+
+  if user_config then
+    vim.g.cp = vim.tbl_deep_extend('force', vim.g.cp or {}, user_config)
+  end
+end
+
 return M

lua/cp/setup.lua

@@ -160,6 +160,8 @@ function M.setup_contest(platform, contest_id, problem_id, language)
     vim.bo[bufnr].buftype = ''
     vim.bo[bufnr].swapfile = false
 
+    state.set_language(lang)
+
     if cfg.hooks and cfg.hooks.setup_code and not vim.b[bufnr].cp_setup_done then
       local ok = pcall(cfg.hooks.setup_code, state)
       if ok then