feat: 添加计算器程序并更新版本至0.2.7

添加新的计算器程序calc.lua，包含完整的计算功能和界面
移除shell.lua中的错误窗口功能，改为直接输出错误信息
更新installer.lua和bios.lua中的版本号至0.2.7
添加calc命令的自动补全功能

data/computercraft/lua/rom/programs/calc.lua

@@ -0,0 +1,89 @@
+-- Calculator program calc.lua
+local term = require("term")
+local keys = require("keys")
+local colors = require("colors")
+
+-- Function to draw top bar
+local function drawTopBar()
+    -- Get terminal size
+    local w, h = term.getSize()
+    
+    -- Save cursor position
+    local cx, cy = term.getCursorPos()
+    
+    -- Set top bar color
+    term.setTextColor(colors.yellow)
+    term.setBackgroundColor(colors.blue)
+    
+    -- Move to top-left corner
+    term.setCursorPos(1, 1)
+    
+    -- Draw top bar with centered title
+    local title = " LeonOS Calculator "
+    local padding = math.floor((w - #title) / 2)
+    term.write(string.rep(" ", padding) .. title .. string.rep(" ", padding))
+    
+    -- Reset colors
+    term.setTextColor(colors.white)
+    term.setBackgroundColor(colors.black)
+    
+    -- Restore cursor position
+    term.setCursorPos(cx, cy)
+end
+
+-- Clear screen and show UI
+term.clear()
+drawTopBar()
+
+-- Move cursor to below top bar and show instructions
+term.setCursorPos(1, 3)
+print("Enter an expression, press Enter to calculate (type 'q' to quit)")
+print("Supports +, -, *, /, ^(exponent), %(modulus), and parentheses")
+print("---------------------------")
+
+while true do
+    -- Show prompt
+    io.write("> ")
+    local input = io.read()
+    
+    -- Check for exit
+    if input == "q" or input == "quit" then
+        break
+    end
+    
+    -- Check for clear screen
+    if input == "clear" then
+        term.clear()
+drawTopBar()
+        -- Move cursor to below top bar and show instructions
+        term.setCursorPos(1, 3)
+        print("Enter an expression, press Enter to calculate (type 'q' to quit)")
+        print("Supports +, -, *, /, ^(exponent), %(modulus), and parentheses")
+        print("---------------------------")
+        goto continue
+    end
+    
+    -- Calculate expression
+    local success, result = pcall(function()
+        -- Replace Chinese parentheses with English ones
+        input = input:gsub("（", "("):gsub("）", ")")
+        -- Safely execute expression
+        local func = load("return " .. input)
+        if func then
+            return func()
+        else
+            error("Invalid expression")
+        end
+    end)
+    
+    -- Show result
+    if success then
+        print("Result: " .. result)
+    else
+        print("Error: " .. tostring(result))
+    end
+    
+    ::continue::
+end
+
+print("Calculator has exited")