fix(tmux): handle \r line endings and missing pane_title in list-panes

[MoerAI]

Summary

• Strip \r characters from list-panes output to handle Windows-style line endings that caused pane rows to be dropped
• Relax field count check from 9 to 8 fields so panes with empty/missing pane_title are still parsed correctly
• This fixes the "first subagent split fails in single-pane session" bug where mainPane resolution failed because all pane rows were dropped by the parser

Root cause: In some environments, tmux list-panes output contains \r\n line endings or empty pane_title values. The parser's split("\n") left trailing \r in field values (corrupting parseInt), and the fields.length < 9 check dropped rows where pane_title was absent.

Fixes #2241

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Summary by cubic

Fix tmux list-panes parsing by removing \r characters and handling missing pane_title. This restores main pane detection and prevents the first subagent split from failing in single-pane sessions.

• Bug Fixes
  • Strip \r from list-panes output to support CRLF line endings.
  • Allow 8 fields and default pane_title to "" so panes aren’t dropped.

^{Written for commit e1952d3. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 1 file

Confidence score: 5/5

• Automated review surfaced no issues in the provided summaries.
• No files require special attention.

_{Auto-approved: The changes correctly handle CRLF line endings and optional pane titles, fixing a bug where valid panes were skipped. Minimal risk as it only improves the robustness of tmux output parsing.}