fix(layout): honour horizontal padding and page origin (S2)

paragraph_layouter placed lines at page.border_size while sizing them to
available_width, which subtracts both paddings. Text therefore started flush
against the left border and the entire padding budget accumulated on the right,
so lines broke well short of the right border.

Page now describes its content box directly - content_origin, content_rect and
remaining_height - and the layouters use it instead of each recomputing the
geometry from border_size. The four block layouters had all been computing
remaining space as size[1] - y_offset - border_size, subtracting the border but
not the bottom padding, so every block type could be placed into the bottom
padding; remaining_height fixes that too.

Page also gains an origin, defaulting to (0, 0). That is inert for a top-level
page but lets a page be positioned inside another surface, which table cells
need in order to be laid out by the normal engine.

Golden images regenerated: content now sits inside the padding on all sides.

pyWebLayout/layout/document_layouter.py

@@ -151,7 +151,7 @@ def paragraph_layouter(paragraph: Paragraph,
             y_cursor = page._current_y_offset
         else:
             y_cursor = page._current_y_offset
-        x_cursor = page.border_size
+        x_cursor = page.content_origin[0]
 
         # Create a temporary Text object to calculate word width
         if word:
@@ -305,7 +305,7 @@ def image_layouter(image: AbstractImage, page: Page, max_width: Optional[int] =
         max_width = page.available_width
 
     # Calculate available height on page
-    available_height = page.size[1] - page._current_y_offset - page.border_size
+    available_height = page.remaining_height
 
     # If no space available, image doesn't fit
     if available_height <= 0:
@@ -325,7 +325,7 @@ def image_layouter(image: AbstractImage, page: Page, max_width: Optional[int] =
         return False
 
     # Create renderable image
-    x_offset = page.border_size
+    x_offset = page.content_origin[0]
     y_offset = page._current_y_offset
 
     # Access page.draw to ensure canvas is initialized
@@ -368,7 +368,7 @@ def table_layouter(
     """
     # Calculate available space
     available_width = page.available_width
-    x_offset = page.border_size
+    x_offset = page.content_origin[0]
     y_offset = page._current_y_offset
 
     # Access page.draw to ensure canvas is initialized
@@ -388,7 +388,7 @@ def table_layouter(
 
     # Check if table fits on current page
     table_height = renderer.size[1]
-    available_height = page.size[1] - y_offset - page.border_size
+    available_height = page.remaining_height
 
     if table_height > available_height:
         return False
@@ -436,7 +436,7 @@ def button_layouter(button: Button,
         font = Font(font_size=14, colour=(255, 255, 255))
 
     # Calculate available space
-    available_height = page.size[1] - page._current_y_offset - page.border_size
+    available_height = page.remaining_height
 
     # Create ButtonText renderable
     button_text = ButtonText(button, font, page.draw, padding=padding)
@@ -447,7 +447,7 @@ def button_layouter(button: Button,
         return False, ""
 
     # Position the button
-    x_offset = page.border_size
+    x_offset = page.content_origin[0]
     y_offset = page._current_y_offset
 
     button_text.set_origin(np.array([x_offset, y_offset]))
@@ -486,7 +486,7 @@ def form_field_layouter(field: FormField, page: Page, font: Optional[Font] = Non
         font = Font(font_size=12, colour=(0, 0, 0))
 
     # Calculate available space
-    available_height = page.size[1] - page._current_y_offset - page.border_size
+    available_height = page.remaining_height
 
     # Create FormFieldText renderable
     field_text = FormFieldText(field, font, page.draw, field_height=field_height)
@@ -497,7 +497,7 @@ def form_field_layouter(field: FormField, page: Page, font: Optional[Font] = Non
         return False, ""
 
     # Position the field
-    x_offset = page.border_size
+    x_offset = page.content_origin[0]
     y_offset = page._current_y_offset
 
     field_text.set_origin(np.array([x_offset, y_offset]))