feat: Add sandbox escape hatches for daemon lock issues (GH #353 Phase 1)

Implements three quick fixes for users stuck in sandboxed environments
(e.g., Codex) where daemon cannot be stopped:

1. **--force flag for bd import**
   - Forces metadata update even when DB is synced with JSONL
   - Fixes stuck state caused by stale daemon cache
   - Shows: "Metadata updated (database already in sync with JSONL)"

2. **--allow-stale global flag**
   - Emergency escape hatch to bypass staleness check
   - Shows warning: "⚠️  Staleness check skipped (--allow-stale)"
   - Allows operations on potentially stale data

3. **Improved error message**
   - Added sandbox-specific guidance to staleness error
   - Suggests --sandbox, --force, and --allow-stale flags
   - Provides clear fix steps for different scenarios

Also fixed:
- Removed unused import in cmd/bd/duplicates_test.go

Follow-up work filed:
- bd-u3t: Phase 2 - Sandbox auto-detection
- bd-e0o: Phase 3 - Daemon robustness enhancements
- bd-9nw: Documentation updates

Fixes #353 (Phase 1)

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

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

cmd/bd/duplicates_test.go

@@ -2,7 +2,6 @@ package main
 
 import (
 	"context"
-	"path/filepath"
 	"testing"
 
 	"github.com/steveyegge/beads/internal/types"