fix: Fix initialization order bug in ScreenshotService

BUG: AttributeError: 'ScreenshotService' object has no attribute '_platform'

Root cause: In __init__, _get_default_save_path() was called BEFORE
_platform was initialized. The method tried to access self._platform
to determine the save path.

FIX: Moved platform detection BEFORE save path initialization in:
- core/screenshot.py
- core/screenshot_secure.py
- core/screenshot_vulnerable.py

Order changed from:
  1. self._save_path = self._get_default_save_path()  # FAILS - needs _platform
  2. self._platform = platform.system().lower()

To:
  1. self._platform = platform.system().lower()
  2. self._save_path = self._get_default_save_path()  # WORKS - _platform exists

This is a common Python initialization order bug where methods called
in __init__ reference attributes that haven't been set yet.

core/screenshot.py

@@ -53,7 +53,6 @@ class ScreenshotService:
         
         # Configuration
         self._auto_save: bool = True
-        self._save_path: Path = self._get_default_save_path()
         self._format: str = "PNG"
         self._quality: int = 95  # For JPEG
         self._history_size: int = 20
@@ -62,10 +61,13 @@ class ScreenshotService:
         self._history: deque = deque(maxlen=self._history_size)
         self._last_screenshot: Optional[Image.Image] = None
         
-        # Platform detection
+        # Platform detection - MUST be before _get_default_save_path()
         self._platform = platform.system().lower()
         self._use_pil = self._platform == "windows"
         
+        # Set save path AFTER platform detection
+        self._save_path: Path = self._get_default_save_path()
+        
         # Lazy init for capture backends
         self._pil_available: Optional[bool] = None
         self._pyautogui_available: Optional[bool] = None

core/screenshot_secure.py

@@ -53,7 +53,6 @@ class ScreenshotService:
         
         # Configuration
         self._auto_save: bool = True
-        self._save_path: Path = self._get_default_save_path()
         self._format: str = "PNG"
         self._quality: int = 95  # For JPEG
         self._history_size: int = 20
@@ -62,10 +61,13 @@ class ScreenshotService:
         self._history: deque = deque(maxlen=self._history_size)
         self._last_screenshot: Optional[Image.Image] = None
         
-        # Platform detection
+        # Platform detection - MUST be before _get_default_save_path()
         self._platform = platform.system().lower()
         self._use_pil = self._platform == "windows"
         
+        # Set save path AFTER platform detection
+        self._save_path: Path = self._get_default_save_path()
+        
         # Lazy init for capture backends
         self._pil_available: Optional[bool] = None
         self._pyautogui_available: Optional[bool] = None

core/screenshot_vulnerable.py

@@ -55,7 +55,6 @@ class ScreenshotService:
         
         # Configuration
         self._auto_save: bool = True
-        self._save_path: Path = self._get_default_save_path()
         self._format: str = "PNG"
         self._quality: int = 95  # For JPEG
         self._history_size: int = 20
@@ -64,10 +63,13 @@ class ScreenshotService:
         self._history: deque = deque(maxlen=self._history_size)
         self._last_screenshot = None
         
-        # Platform detection
+        # Platform detection - MUST be before _get_default_save_path()
         self._platform = platform.system().lower()
         self._use_pil = self._platform == "windows"
         
+        # Set save path AFTER platform detection
+        self._save_path: Path = self._get_default_save_path()
+        
         # Lazy init for capture backends
         self._pil_available: Optional[bool] = None
         self._pyautogui_available: Optional[bool] = None