fix(taskctl): fix adversarial worktree directory, resilient branch creation (#381, #382, #383)

[randomm]

Summary

Fixes three taskctl pipeline bugs that prevented autonomous development from working reliably.

#383 — developer-pipeline starts in main worktree instead of assigned worktree:

• Root cause: spawnAdversarial used parentSession.directory (PM session dir = main repo) instead of safeWorktree
• Fix: Changed directory: parentSession.directory → directory: safeWorktree on line 370
• This also fixes fix(taskctl): Pulse not detecting commits in worktrees causing adversarial never to spawn #382 since the adversarial now operates in the correct worktree

#382 — Pulse not detecting commits in worktrees causing adversarial never to spawn:

• Root cause was fix(taskctl): developer-pipeline starts in main worktree instead of assigned worktree #383 — adversarial ran in wrong directory, so git diff found no changes in main repo
• hasCommittedChanges was already receiving the correct worktree path; the bug was downstream in the adversarial session

#381 — Make start command resilient to existing branches:

• Root cause: git checkout -b fails if branch already exists from a previous failed run
• Fix: Check if branch exists with git rev-parse --verify, checkout existing branch instead of creating
• Handle remote branch already exists by setting upstream instead of failing

Fixes #381
Fixes #382
Fixes #383