fix(tmux): add barrel export for pane-state-parser and log parse failures

[code-yeongyu]

Fixes regression from #2453: barrel export missing + silent parse failure

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Summary by cubic

Fixes regression from #2453 by restoring the pane-state-parser barrel export and adding logging for pane state parse failures. This resolves missing exports and surfaces parse issues for easier debugging.

• Bug Fixes
  • Re-export pane-state-parser from src/features/tmux-subagent/index.ts.
  • Log parse failures in pane-state-querier with sourcePaneId to avoid silent failures.

^{Written for commit 899d265. Summary will update on new commits.}

[cubic-dev-ai]

No issues found across 2 files

Confidence score: 5/5

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

_{Auto-approved: Fixes a regression by restoring a missing barrel export and adding low-risk logging for debugging. Minimal logic changes.}