af cleanup doesn't kill shellper processes — orphaned processes accumulate

[waleedkadous]

Problem

When af cleanup --project N runs, it:

• Removes the worktree
• Deletes local and remote branches
• Kills the Tower terminal registration

But it does NOT kill the shellper process. The shellper continues running as an orphan, consuming resources. After cleaning up 6 builders, 20+ orphaned shellper processes were found still running.

Repro

1. af spawn 100 --protocol bugfix
2. Wait for builder to complete
3. af cleanup --project 100
4. ps aux | grep shellper | grep 100 — process still running

Expected

af cleanup should kill the shellper process (and any child processes like claude) before removing the worktree.

Where to Look

• packages/codev/src/agent-farm/commands/cleanup.ts — cleanup logic
• packages/codev/src/terminal/session-manager.ts — session teardown
• The cleanup code calls killTowerTerminal() but this only removes the Tower registration, it doesn't send a kill signal to the shellper process

[waleedkadous]

On it! Working on a fix now.