feat: Implement core functionality for DTC C/C++ IDE

- Added ProjectManager class to handle project operations including opening, closing, building, and running projects.
- Introduced SyntaxHighlighter class for syntax highlighting in C and C++ files.
- Developed TerminalWidget for command execution and output display.
- Created TextEditor with line numbering and auto-indentation features.
- Established main application entry point in main.cpp.
- Designed UI layout for MainWindow using Qt Designer.

include/TextEditor.h

@@ -0,0 +1,77 @@
+#pragma once
+
+#include <QtWidgets/QPlainTextEdit>
+#include <QtCore/QTextStream>
+#include <QtGui/QTextDocument>
+#include <QtGui/QTextCursor>
+#include <QtGui/QKeyEvent>
+#include <QtCore/QTimer>
+
+class SyntaxHighlighter;
+
+class TextEditor : public QPlainTextEdit
+{
+    Q_OBJECT
+    friend class LineNumberArea;
+
+public:
+    explicit TextEditor(QWidget *parent = nullptr);
+    ~TextEditor();
+
+    void setFilePath(const QString &filePath);
+    QString filePath() const;
+    
+    bool isModified() const;
+    void setModified(bool modified);
+    
+    bool loadFile(const QString &filePath);
+    bool saveFile();
+    bool saveAsFile(const QString &filePath);
+
+    void setLineNumberAreaWidth(int width);
+    void updateLineNumberArea(const QRect &rect, int dy);
+
+signals:
+    void fileModified(bool modified);
+    void cursorPositionChanged(int line, int column);
+
+protected:
+    void keyPressEvent(QKeyEvent *event) override;
+    void paintEvent(QPaintEvent *event) override;
+    void resizeEvent(QResizeEvent *event) override;
+
+private slots:
+    void highlightCurrentLine();
+    void updateCursorPosition();
+    void autoIndent();
+
+private:
+    void setupEditor();
+    void updateLineNumberAreaWidth(int newBlockCount);
+
+public:
+    int lineNumberAreaWidth();
+
+    QString m_filePath;
+    bool m_isModified;
+    SyntaxHighlighter *m_syntaxHighlighter;
+    QWidget *m_lineNumberArea;
+    QTimer *m_autoSaveTimer;
+};
+
+// Line number area widget
+class LineNumberArea : public QWidget
+{
+public:
+    LineNumberArea(TextEditor *editor) : QWidget(editor), m_textEditor(editor) {}
+
+    QSize sizeHint() const override {
+        return QSize(m_textEditor->lineNumberAreaWidth(), 0);
+    }
+
+protected:
+    void paintEvent(QPaintEvent *event) override;
+
+private:
+    TextEditor *m_textEditor;
+};