fix(context): add missing function after rebase

clear_subagents and clear_subagents were missing after rebase

This causes history navigation to throw an error

Author: sudo-tee

lua/opencode/context.lua

@@ -143,6 +143,10 @@ function M.remove_file(file)
   state.context_updated_at = vim.uv.now()
 end
 
+function M.clear_files()
+  M.context.mentioned_files = nil
+end
+
 function M.add_subagent(subagent)
   if not M.context.mentioned_subagents then
     M.context.mentioned_subagents = {}
@@ -168,6 +172,10 @@ function M.remove_subagent(subagent)
   state.context_updated_at = vim.uv.now()
 end
 
+function M.clear_subagents()
+  M.context.mentioned_subagents = nil
+end
+
 ---@param opts? OpencodeContextConfig
 function M.delta_context(opts)
   opts = opts or config.context