Combines three related sling improvements:
1. Auto-attach mol-polecat-work (Issue #288)
- Automatically attach work molecule when slinging to polecats
- Ensures polecats have standard guidance molecule attached
2. Fix polecat hook with molecule (Issue #197)
- Use beads.ResolveHookDir() for correct directory resolution
- Prevents bd cook from failing in polecat worktree
3. Spawn fresh polecat when target has no session
- When slinging to a dead polecat, spawn fresh one instead of failing
- Fixes stale convoys not progressing due to done polecats
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