feat: Add regex extract mode and append suffix to EPG mapping

[Warbs816]

Summary

• Adds a regex extract mode toggle to EPG mapping advanced settings — when enabled, the first capture group from the regex pattern is used as the channel value instead of removing the match (e.g. (?<![A-Z])([A-Z]{4})(?![A-Z]) on CBS 123 (OHIU) Local extracts OHIU)
• Adds an append suffix text field that appends text to cleaned channel values before EPG lookup (e.g. appending -DT to get OHIU-DT)
• No migrations needed — settings stored in existing JSON settings column on epg_maps

Closes #423

Test plan

• Create an EPG map with regex enabled + extract mode on, using a capture group pattern
• Verify the extracted value is used for matching instead of removing the match
• Add an append suffix and verify it's appended before EPG lookup
• Verify default regex mode (extract off) still removes matched text as before
• Verify append suffix works independently without regex