Fix tmux session startup and config escape sequences

[mackermedia]

Summary

• Improved tmux session startup error handling with more detailed error messages
• Added automatic cleanup of ANSI escape sequences in config files to prevent parsing errors

Changes

1. Enhanced tmux session error handling

• Added program existence check before attempting to create tmux session
• Improved error messages with more context (session name, program, directory)
• Better stderr capture and reporting

2. Config file escape sequence cleanup

• Added cleanEscapeSequences function to remove ANSI escape codes from raw JSON
• Added cleanProgramPath function to extract clean paths from escape-wrapped strings
• Auto-saves cleaned config when escape sequences are detected
• Prevents future parsing errors from terminal color codes in config

Test plan

• Test tmux session creation with non-existent program
• Test config loading with escape sequences in JSON
• Verify cleaned config is saved correctly
• Run gofmt to ensure code formatting

Context

This PR addresses issues where:

1. Users would see generic "Failed to start new session" errors without understanding why
2. Config files could become corrupted with ANSI escape sequences from terminal output

🤖 Generated with Claude Code

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[mackermedia]

I have read the CLA Document and I hereby sign the CLA