doc: Document main_test.go refactoring analysis (bd-1rh)

Analysis shows main_test.go is NOT a good candidate for shared DB pattern
due to global state manipulation and integration test characteristics.

Changes:
- Added MAIN_TEST_REFACTOR_NOTES.md documenting findings
- Fixed unused import in duplicates_test.go (from recent pull)

Key findings:
- 18 tests with 14 newTestStore() calls
- Tests manipulate global state (autoFlushEnabled, isDirty, etc.)
- Tests simulate workflows (flush, import) not just CRUD
- Shared DB causes deadlocks between flush ops and cleanup
- Integration tests need process-level isolation

Recommendation: Leave as-is or use Option 2 (grouped tests without
shared DB). Focus P2 efforts on integrity_test.go instead.

🤖 Generated with 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"