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/main.go

@@ -89,6 +89,7 @@ var (
 	noAutoFlush  bool
 	noAutoImport bool
 	sandboxMode  bool
+	allowStale   bool // Use --allow-stale: skip staleness check (emergency escape hatch)
 	noDb         bool // Use --no-db mode: load from JSONL, write back after each command
 	profileEnabled bool
 	profileFile    *os.File
@@ -109,6 +110,7 @@ func init() {
 	rootCmd.PersistentFlags().BoolVar(&noAutoFlush, "no-auto-flush", false, "Disable automatic JSONL sync after CRUD operations")
 	rootCmd.PersistentFlags().BoolVar(&noAutoImport, "no-auto-import", false, "Disable automatic JSONL import when newer than DB")
 	rootCmd.PersistentFlags().BoolVar(&sandboxMode, "sandbox", false, "Sandbox mode: disables daemon and auto-sync")
+	rootCmd.PersistentFlags().BoolVar(&allowStale, "allow-stale", false, "Allow operations on potentially stale data (skip staleness check)")
 	rootCmd.PersistentFlags().BoolVar(&noDb, "no-db", false, "Use no-db mode: load from JSONL, no SQLite")
 	rootCmd.PersistentFlags().BoolVar(&profileEnabled, "profile", false, "Generate CPU profile for performance analysis")