Add configurable font size and row height for commit table

[Pwuts]

Summary

• Adds two new settings under Git-graph > Graph:
  • git-graph.graph.fontSize — font size in pixels (default: 13, range: 8–24)
  • git-graph.graph.rowHeight — row height in pixels (default: 24, range: 16–48)
• The graph canvas grid is automatically derived from the row height setting, so the graph lines stay aligned with the table rows
• CSS uses custom properties with sensible fallbacks

Test plan

• Open settings, search "git graph font size" and "git graph row height" — both appear under Git-graph > Graph
• Change row height (e.g. to 32) → reload Git Graph → rows are taller, graph lines align
• Change font size (e.g. to 16) → reload Git Graph → text is larger
• Default values (13px font, 24px row height) match the original appearance

🤖 Generated with Claude Code

[Pwuts]

Before (13/24px; default)

After (14/28px)