Session lifecycle: fix name reuse, deduplication, and session_key rotation

[alexsiri7]

Fix several session lifecycle bugs that cause agent spawning failures and stale sessions:

• Closed session beads never block session name reuse (most impactful — blocks agent restarts)
• Allow configured named sessions to reclaim their own alias and name
• Repair adoption-then-orphan bug in session bead deduplication
• Prevent duplicate session bead creation on alias sync failure
• Allow closed session beads to release their explicit name for reuse
• Rotate session_key for wake_mode=fresh agents to prevent conversation resumption
• Clear session_key on drain-ack/restart-requested so next wake starts fresh
• Drain order_dispatch goroutines before one-shot controller exit
• Output valid JSON when --json flag used with no sessions found

These fixes address the 'session alias already exists' errors that prevent agents from restarting after crashes.