Fix SGR pattern regex to correctly match ANSI escape sequences

[assisted-by-ai]

Summary

Fixed the regular expression pattern used to match Select Graphic Rendition (SGR) ANSI escape sequences. The previous pattern had incorrect grouping that could fail to match valid SGR sequences.

Key Changes

• Restructured the SGR regex pattern in get_sgr_pattern() to correctly handle optional semicolons and SGR codes
• Changed from (;*({sgr_combo})?(;+{sgr_combo})*)?;*m to ;*({sgr_combo}(;+{sgr_combo})*;*)?m
• The new pattern ensures that:
  • Leading semicolons are matched before the group
  • At least one SGR code is required when the optional group is present
  • Trailing semicolons are included within the group
  • The pattern correctly validates ANSI escape sequence format

Implementation Details

This change improves the robustness of ANSI escape sequence parsing by fixing the quantifier placement and grouping logic, ensuring that malformed or edge-case SGR sequences are handled more predictably.

https://claude.ai/code/session_01QhhwK5uJq7Rv2ekDCt5aZ9

[ArrayBolt3]

Appears identical to assisted-by-ai#14, accepted already.