fix(opencode): coordinate worktree bootstrap cleanup

[LeXwDeX]

Summary

• make Worktree own asynchronous bootstrap and reset start fibers
• serialize create, remove, and reset per canonical worktree path
• interrupt in-flight startup commands before destructive cleanup
• keep different worktrees independent

Incident

Main CI run 31364499143 hung after worktree.remove because an asynchronous bootstrap process could outlive directory cleanup.

TDD evidence

• deterministic remove/start-process red to green
• deterministic reset/start-process regression
• deterministic concurrent create/remove red to green
• deterministic same-worktree destructive-operation serialization

Verification

• Worktree and endpoint tests: 24 pass, 0 fail
• HttpAPI coverage/auth/effect: 227 pass, 0 fail in each mode
• repository typecheck: 29/29
• lint: 4852 warnings, 0 errors (ratchet pass)
• Standards review: 0 findings
• Spec review: 0 findings