fix(session): derived session resume command broken due to file path mismatch

[SurviveM]

Requirement

buildResumeCommand generates resume commands pointing to native tool scan paths, but derived sessions are stored in ~/.codexmate/sessions/derived/{codex|claude}/. Both codex resume and claude -r cannot locate derived files. Before resume, detect if session is derived; if so, copy/symlink to native path first, or provide codexmate resume <session-id> as unified entry that handles path mapping internally.

Verification

1. Derive a Claude session from Codex session -> click "Copy Resume Command" -> run claude -r <id> -> Claude loads and continues conversation
2. Derive a Codex session from Claude session -> run codex resume <id> -> Codex loads successfully
3. Derived session resume success rate matches native session resume rate