Add breaking change summary for regex flag removal

[Copilot]

Responded to maintainer request to document the breaking change introduced in the PR.

Changes:

• Added comprehensive summary explaining the removal of regex: true/false flag from required_text and forbidden_text patterns
• Documented the new simplified syntax where string form ("text") implies literal substring matching and object form ({pattern: "..."}) implies regex matching
• Provided before/after examples and migration guidance

Example:

# Before (old syntax with explicit regex flag)
required_text:
  - { pattern: "example", regex: false }
  - { pattern: "v\\d+\\.\\d+", regex: true }

# After (new syntax - form determines behavior)
required_text:
  - "example"  # string form = literal match
  - { pattern: "v\\d+\\.\\d+" }  # object form = regex match

The breaking change simplifies the API by removing redundant configuration - the syntax form itself now determines matching behavior.

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