Fix cursor/background vertical alignment in SVG screenshots

- Remove dominant-baseline: text-before-edge (has Safari compatibility issues)
- Use separate y positions for rect (top of cell) and text (baseline)
- rect_y = padding + row * line_height (top of cell)
- text_y = rect_y + font_size (alphabetic baseline position)

This ensures background rects and text are properly aligned across all
browsers, fixing the half-line vertical offset on cursor blocks.

tests/test_svg_exporter.py

@@ -152,8 +152,6 @@ class TestRenderTerminalSvg:
     def test_css_properties(self) -> None:
         """SVG includes essential CSS properties for proper rendering."""
         svg = render_terminal_svg([], width=80, height=24)
-        # Check for proper baseline alignment
-        assert "dominant-baseline: text-before-edge" in svg
         # Check for legibility optimization
         assert "text-rendering: optimizeLegibility" in svg
         # Check for monospace font