When tasks fail and retry, the old worktree lingered on disk and the new
worktree got a random name causing worktrunk to report it as unassigned.
Now: retry clears worktree/branch fields, removes old worktree from disk,
and createWorktree returns the actual branch name (including -2 suffixes)
so task.branch always matches reality.
Also fixes pre-existing test failures: Terminal WebSocket mock sessions
missing lastActivityAt, and TerminalModal keyboard overlap tests leaking
cached _initialViewportHeight between tests.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
c79aec6d3e