Add URL whitelist enforcement for Kiosk-mode and enhance configuration management

- Introduced `allowed_urls` in configuration to specify whitelisted domains/patterns.
- Implemented `RestrictedWebEngineView` to enforce URL restrictions in the web view.
- Updated `MainWindow` to utilize the new restricted web view and added navigation toolbar.
- Enhanced unit tests for configuration and restricted web view to cover new functionality.

tests/unit/test_config.py

@@ -46,6 +46,7 @@ class TestConfigFromEnv:
             f"LOG_LEVEL=DEBUG\n"
             f"LOG_FILE={tmp_path / 'test.log'}\n"
             f"ALLOWED_ROOTS={root1},{root2}\n"
+            f"ALLOWED_URLS=example.com,*.test.org\n"
             f"WEBAPP_URL=http://localhost:8000\n"
             f"WINDOW_WIDTH=1200\n"
             f"WINDOW_HEIGHT=800\n"
@@ -58,6 +59,7 @@ class TestConfigFromEnv:
         assert config.app_version == "2.0.0"
         assert config.log_level == "DEBUG"
         assert config.allowed_roots == [root1.resolve(), root2.resolve()]
+        assert config.allowed_urls == ["example.com", "*.test.org"]
         assert config.webapp_url == "http://localhost:8000"
         assert config.window_width == 1200
         assert config.window_height == 800
@@ -146,3 +148,39 @@ class TestConfigValidation:
         assert len(config.allowed_roots) == 2
         assert config.allowed_roots[0] == dir1.resolve()
         assert config.allowed_roots[1] == dir2.resolve()
+
+    def test_allowed_urls_empty(self, tmp_path):
+        """Test that empty ALLOWED_URLS means no URL restriction."""
+        env_file = tmp_path / ".env"
+        env_file.write_text("ALLOWED_URLS=\n")
+
+        config = Config.from_env(str(env_file))
+
+        assert config.allowed_urls == []
+
+    def test_allowed_urls_single(self, tmp_path):
+        """Test loading single allowed URL."""
+        env_file = tmp_path / ".env"
+        env_file.write_text("ALLOWED_URLS=example.com\n")
+
+        config = Config.from_env(str(env_file))
+
+        assert config.allowed_urls == ["example.com"]
+
+    def test_allowed_urls_multiple(self, tmp_path):
+        """Test loading multiple allowed URLs."""
+        env_file = tmp_path / ".env"
+        env_file.write_text("ALLOWED_URLS=example.com,*.test.org,localhost\n")
+
+        config = Config.from_env(str(env_file))
+
+        assert config.allowed_urls == ["example.com", "*.test.org", "localhost"]
+
+    def test_allowed_urls_with_whitespace(self, tmp_path):
+        """Test that whitespace is trimmed from allowed URLs."""
+        env_file = tmp_path / ".env"
+        env_file.write_text("ALLOWED_URLS= example.com , test.org \n")
+
+        config = Config.from_env(str(env_file))
+
+        assert config.allowed_urls == ["example.com", "test.org"]