Tower should auto-reconnect to surviving tmux sessions on startup

[waleedkadous]

Summary

When the tower restarts, builder tmux sessions survive (tmux is a separate process), but the node-pty connections are lost. Currently builders must be manually resumed with af spawn --issue N --resume. The tower should automatically reconnect to surviving sessions on startup.

Current Behavior

1. Tower stops → node-pty connections die
2. tmux sessions survive independently
3. Tower restarts → SQLite still has session rows, but no PTY connections
4. Builder is dead until user manually runs af spawn --resume

Desired Behavior

1. Tower stops → node-pty connections die
2. tmux sessions survive independently
3. Tower restarts → reconcileTerminalSessions() runs:
   • Query SQLite terminal_sessions table for active sessions
   • For each session, check if tmux session exists (tmux has-session -t <name>)
   • If alive: spawn new node-pty attached to the surviving tmux session, update SQLite
   • If dead: clean up stale SQLite row
4. Builders continue working without manual intervention

Context

• SQLite is the source of truth for terminal sessions (Spec 0090)
• tmux session names follow a known pattern: builder-<project>-<id>, architect-<project>, shell-<project>-<n>
• node-pty can attach to existing tmux sessions via tmux attach-session -t <name>
• The reconcileTerminalSessions() concept exists in the architecture docs but isn't implemented yet

Notes

This would make af tower stop && af tower start (e.g., after rebuilding) seamless for active builders. Currently every tower restart requires manually resuming each builder.

[waleedkadous]

On it! Working on a fix now.