Configure Gitea Workflows and Add Build Scripts

- Update build-linux.yaml to use standard Ubuntu runner.
- Update build-windows.yaml to use tobix/pywine container for cross-compilation on Linux.
- Add build_app.py and check_ttx6.py helper scripts.

build_app.py

@@ -0,0 +1,60 @@
+import sys
+import os
+import subprocess
+import shutil
+import platform
+
+def clean_build_dirs():
+    """Removes build and dist directories if they exist."""
+    for d in ["build", "dist"]:
+        if os.path.exists(d):
+            print(f"Cleaning {d}...")
+            shutil.rmtree(d)
+    
+    spec_file = "TeletextEditor_Linux.spec" if platform.system() == "Linux" else "TeletextEditor_Windows.spec"
+    if os.path.exists(spec_file):
+        os.remove(spec_file)
+
+def build():
+    system = platform.system()
+    print(f"Detected OS: {system}")
+
+    base_cmd = [
+        sys.executable, "-m", "PyInstaller",
+        "--onefile",
+        "--windowed",
+        "--paths", "src",
+        "src/main.py"
+    ]
+
+    if system == "Linux":
+        name = "TeletextEditor_Linux"
+    elif system == "Windows":
+        name = "TeletextEditor_Windows.exe"
+    else:
+        print(f"Unsupported platform: {system}")
+        return
+
+    cmd = base_cmd + ["--name", name]
+
+    print("Running build command:")
+    print(" ".join(cmd))
+
+    try:
+        subprocess.check_call(cmd)
+        print("\n" + "="*40)
+        print(f"Build successful! Executable is in 'dist/{name}'")
+        print("="*40)
+    except subprocess.CalledProcessError as e:
+        print(f"Build failed with error code {e.returncode}")
+        sys.exit(1)
+
+    # Cross-compilation note
+    if system == "Linux":
+        print("\nNote: To build the Windows executable, please run this script on Windows.")
+    elif system == "Windows":
+        print("\nNote: To build the Linux executable, please run this script on Linux.")
+
+if __name__ == "__main__":
+    clean_build_dirs()
+    build()