feat: implement ephemeral polecat model

This implements the ephemeral polecat model where polecats are spawned
fresh for each task and deleted upon completion.

Key changes:

**Spawn (internal/cmd/spawn.go):**
- Always create fresh worktree from main branch
- Run bd init in new worktree to initialize beads
- Remove --create flag (now implicit)
- Replace stale polecats with fresh worktrees

**Handoff (internal/cmd/handoff.go):**
- Add rig/polecat detection from environment and tmux session
- Send shutdown requests to correct witness (rig/witness)
- Include polecat name in lifecycle request body

**Witness (internal/witness/manager.go):**
- Add mail checking in monitoring loop
- Process LIFECYCLE shutdown requests
- Implement full cleanup sequence:
  - Kill tmux session
  - Remove git worktree
  - Delete polecat branch

**Polecat state machine (internal/polecat/types.go):**
- Primary states: working, done, stuck
- Deprecate idle/active (kept for backward compatibility)
- New polecats start in working state
- ClearIssue transitions to done (not idle)

**Polecat commands (internal/cmd/polecat.go):**
- Update list to show "Active Polecats"
- Normalize legacy states for display
- Add deprecation warnings to wake/sleep commands

Closes gt-7ik

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/polecat/manager.go

@@ -80,12 +80,12 @@ func (m *Manager) Add(name string) (*Polecat, error) {
 		return nil, fmt.Errorf("creating worktree: %w", err)
 	}
 
-	// Create polecat state
+	// Create polecat state - ephemeral polecats start in working state
 	now := time.Now()
 	polecat := &Polecat{
 		Name:      name,
 		Rig:       m.rig.Name,
-		State:     StateIdle,
+		State:     StateWorking,
 		ClonePath: polecatPath,
 		Branch:    branchName,
 		CreatedAt: now,
@@ -204,6 +204,7 @@ func (m *Manager) AssignIssue(name, issue string) error {
 }
 
 // ClearIssue removes the issue assignment from a polecat.
+// In the ephemeral model, this transitions to Done state for cleanup.
 func (m *Manager) ClearIssue(name string) error {
 	polecat, err := m.Get(name)
 	if err != nil {
@@ -211,38 +212,44 @@ func (m *Manager) ClearIssue(name string) error {
 	}
 
 	polecat.Issue = ""
-	polecat.State = StateIdle
+	polecat.State = StateDone
 	polecat.UpdatedAt = time.Now()
 
 	return m.saveState(polecat)
 }
 
 // Wake transitions a polecat from idle to active.
+// Deprecated: In the ephemeral model, polecats start in working state.
+// This method is kept for backward compatibility with existing polecats.
 func (m *Manager) Wake(name string) error {
 	polecat, err := m.Get(name)
 	if err != nil {
 		return err
 	}
 
-	if polecat.State != StateIdle {
+	// Accept both idle and done states for legacy compatibility
+	if polecat.State != StateIdle && polecat.State != StateDone {
 		return fmt.Errorf("polecat is not idle (state: %s)", polecat.State)
 	}
 
-	return m.SetState(name, StateActive)
+	return m.SetState(name, StateWorking)
 }
 
 // Sleep transitions a polecat from active to idle.
+// Deprecated: In the ephemeral model, polecats are deleted when done.
+// This method is kept for backward compatibility.
 func (m *Manager) Sleep(name string) error {
 	polecat, err := m.Get(name)
 	if err != nil {
 		return err
 	}
 
-	if polecat.State != StateActive {
+	// Accept working state as well for legacy compatibility
+	if polecat.State != StateActive && polecat.State != StateWorking {
 		return fmt.Errorf("polecat is not active (state: %s)", polecat.State)
 	}
 
-	return m.SetState(name, StateIdle)
+	return m.SetState(name, StateDone)
 }
 
 // saveState persists polecat state to disk.
@@ -268,10 +275,11 @@ func (m *Manager) loadState(name string) (*Polecat, error) {
 	if err != nil {
 		if os.IsNotExist(err) {
 			// Return minimal polecat if state file missing
+			// Use StateWorking since ephemeral polecats are always working
 			return &Polecat{
 				Name:      name,
 				Rig:       m.rig.Name,
-				State:     StateIdle,
+				State:     StateWorking,
 				ClonePath: m.polecatDir(name),
 			}, nil
 		}