feat: Add text_align option to Style

[davefowler]

Summary

Add a text_align option to the Style class to control horizontal text alignment.

Use Case

When embedding mdsvg output in larger SVG compositions (like dashboards), callers often need to align text. Currently this requires hacky string manipulation:

# Current workaround in dataface
aligned_title = title_svg.replace("<text", f'<text text-anchor="{title_anchor}"')

Proposed API

from mdsvg import Style, render

# Option 1: Style parameter
style = Style(text_align="center")  # "left", "center", "right"
svg = render("# Title", style=style)

# Option 2: Render parameter
svg = render("# Title", text_align="center")

Implementation Notes

• Map text_align to SVG text-anchor attribute:
  • "left" → text-anchor="start"
  • "center" → text-anchor="middle"
  • "right" → text-anchor="end"
• Apply to all <text> elements in the output
• Default to "left" (current behavior)

@cursor Instructions

1. Add text_align: str = "left" to the Style class
2. In the SVGRenderer, apply text-anchor attribute based on text_align value
3. Add tests for left/center/right alignment
4. Update README with example

[davefowler]

@cursor please implement this feature. Start by adding the text_align field to Style class.

[cursor]

I've implemented the text_align feature for the Style class. Here's a summary of the changes:

Changes made:

1. src/mdsvg/style.py:

   • Added TextAlign literal type ("left" | "center" | "right")
   • Added text_align: TextAlign = "left" field to the Style class
   • Added get_text_anchor() helper method that maps text_align values to SVG text-anchor values (left→start, center→middle, right→end)

2. src/mdsvg/renderer.py:

   • Updated _render_text_block() to calculate x position based on alignment
   • Added text-anchor attribute to all rendered <text> elements

3. src/mdsvg/__init__.py:

   • Exported TextAlign and CodeBlockOverflow types for users

4. tests/test_renderer.py:

   • Added TestTextAlignment class with 6 tests covering default alignment, center, right, left (explicit), heading alignment, and the helper method

5. README.md:

   • Added "Text Alignment" section with usage examples
   • Added text_align to the style options table

All 129 tests pass and the linter/type checker report no issues.