Use full-bleed photos with a single-line bottom watermark

pigway_frame_flow/renderers/photo_layout.py

@@ -0,0 +1,25 @@
+"""Layout-only extension point for a future AI layout provider."""
+
+from dataclasses import dataclass
+from typing import Protocol
+
+
+@dataclass(frozen=True)
+class PhotoLayout:
+    footer_height: int
+    font_size: int
+    margin: int
+
+
+class PhotoLayoutProvider(Protocol):
+    def layout(self, size: tuple[int, int], caption: dict[str, str]) -> PhotoLayout: ...
+
+
+class WatermarkLayout:
+    def layout(self, size: tuple[int, int], caption: dict[str, str]) -> PhotoLayout:
+        width, height = size
+        return PhotoLayout(
+            footer_height=max(60, round(min(width, height) * 0.06)),
+            font_size=max(24, round(min(width, height) * 0.03)),
+            margin=max(24, round(width * 0.025)),
+        )