feat: start lang refactor

lua/cp/config.lua

@@ -351,6 +351,50 @@ function M.get_config()
   return current_config or M.defaults
 end
 
+---Validate and get effective language config for a platform
+---@param platform_id string
+---@param language_id string
+---@return { valid: boolean, effective?: CpLanguage, extension?: string, error?: string }
+function M.get_language_for_platform(platform_id, language_id)
+  local cfg = M.get_config()
+
+  if not cfg.platforms[platform_id] then
+    return { valid = false, error = string.format("Unknown platform '%s'", platform_id) }
+  end
+
+  if not cfg.languages[language_id] then
+    return { valid = false, error = string.format("Unknown language '%s'", language_id) }
+  end
+
+  local platform = cfg.platforms[platform_id]
+  if not vim.tbl_contains(platform.enabled_languages, language_id) then
+    local available = table.concat(platform.enabled_languages, ', ')
+    return {
+      valid = false,
+      error = string.format(
+        "Language '%s' not enabled for %s. Available: %s",
+        language_id,
+        platform_id,
+        available
+      ),
+    }
+  end
+
+  local effective = cfg.runtime.effective[platform_id][language_id]
+  if not effective then
+    return {
+      valid = false,
+      error = string.format('No effective config for %s/%s', platform_id, language_id),
+    }
+  end
+
+  return {
+    valid = true,
+    effective = effective,
+    extension = effective.extension,
+  }
+end
+
 ---@param contest_id string
 ---@param problem_id? string
 ---@return string