Add screenshot-driven inventory recognition (v0.2.0)

- New ScreenshotFrame: capture screen / load PNG, two-click bbox,
  threaded template matching, editable preview grid for corrections
- ManualFrame kept as second tab for users who prefer typing counts
- capture.py: screen grab via mss (cross-platform)
- requirements: add mss>=6.0 for screen capture support

Closes the gap from v0.1.0 where users had to manually count
every slab — now they aim, click two corners, and edit any
mis-recognized cell.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

sephiria_inv/capture.py

@@ -0,0 +1,43 @@
+"""Screen capture utility.
+
+`capture_screen()` grabs the current screen via mss and returns a PIL RGB
+image. Bounding-box selection of the inventory area is done in the GUI by
+two clicks (top-left + bottom-right) — far more reliable than heuristic
+auto-detection across the many possible game UI scales and DPI settings.
+"""
+
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Tuple
+
+from PIL import Image
+
+
+@dataclass
+class GridBBox:
+    left: int
+    top: int
+    right: int
+    bottom: int
+
+    def as_tuple(self) -> Tuple[int, int, int, int]:
+        return (self.left, self.top, self.right, self.bottom)
+
+
+def capture_screen(monitor: int = 1) -> Image.Image:
+    """Capture the full screen of the given monitor as a PIL RGB image.
+
+    monitor=0 = all monitors combined, 1 = primary on most systems. Falls
+    back to monitor 0 if the requested index is missing.
+    """
+    import mss  # lazy: keep mss optional for renderer/CLI-only use
+
+    with mss.mss() as sct:
+        try:
+            mon = sct.monitors[monitor]
+        except IndexError:
+            mon = sct.monitors[0]
+        shot = sct.grab(mon)
+        img = Image.frombytes("RGB", shot.size, shot.bgra, "raw", "BGRX")
+    return img