Fix chart/risk table misalignment with ggplot2 >= 3.5.0 (#649, #675)

[kassambara]

Summary

• Replace hardcoded grob width indices [2:5] with dynamic panel detection
• Ensure proper chart/risk table alignment across ggplot2 versions >= 3.5.0
• Maintain backward compatibility with older ggplot2 versions

Test plan

• Verify alignment works with ggplot2 3.5.2+
• Run existing test suite (15 tests pass)
• Test basic and complex ggsurvplot scenarios
• Confirm no regressions introduced

Fixes #649 and #675