Force-remove stuck worktrees, with new safety checks and CLI/fleet-view support

What

• Job/session deletion logic now supports an explicit force-remove path for a worktree's directory, used when the normal removal (via git or the WorktreeRemove hook) can't clean it up.
• Before force-removing, Claude Code checks for nested git repositories, tracked (not just uncommitted) changes, and verifies the worktree is actually registered in git's own worktree list; the worktree-state check now separately reports trackedChanges (real edits) versus plain dirty (which includes untracked files).
• If removal is still withheld, the reason is one of tracked_changes, nested_repositories, nested_unverified, or not_registered, and a new aFt message generator produces detailed explanations for every possible refusal reason (dirty, unpushed, unpushed_shared, in_use, live_lock, occupied, shared_record, records_unreadable, unverified, identity_changed, and the remove_failed sub-reasons above).
• The claude rm CLI command gains two new flags: --discard-unpushed <commit>@<worktree-id> to discard unpushed/uncommitted changes on a worktree still at a given commit, and --force-remove-worktree <worktree-id> to force-delete a worktree directory.
• The fleet view's job-delete action gained a second confirm-and-retry path for force-removing a worktree (alongside the existing 'discard unpushed changes' offer), and reports whether the branch was preserved.
• Deletion telemetry and results now distinguish a forced removal from the existing 'left worktree in place' outcome, via a new worktree_force_removed event and a forcedWorktreeRemoval/forceRemoveWithheld result field.

Why

Worktrees (the separate folders git uses for each session's checkout) can get stuck when git or a cleanup hook can't remove them, blocking session/job deletion. This gives users and the CLI an explicit, safety-checked way to force the removal through instead of leaving orphaned directories behind, while refusing to blow away directories with nested repos or real tracked changes without being told to.