fix(lpend): prefer fresh claude session path when registry is stale

[bookandlover]

Summary

Fixes stale lpend/pend claude reads when registry and .claude-session disagree on claude_session_path.

Fixes #95

Root cause

bin/lpend previously selected:

• log_path = registry_log_path or session_log_path

So any non-empty registry path always won, even if stale.

Changes

• Add conflict-aware path selection:
  • If registry/session paths are both present and differ, compare mtime and prefer newer path.
  • Keep existing fallback behavior when only one path exists.
• Add self-healing sync:
  • When selecting .claude-session path, update registry providers.claude.claude_session_path via upsert_registry.
• Keep behavior transparent with debug logs (LPEND_DEBUG / CCB_DEBUG).

Validation

• python3 -m py_compile bin/lpend
• Manual conflict scenario validation (stale registry path + newer .claude-session path):
  • lpend now selects the newer session path.
  • Registry is auto-updated to the selected fresh path.