Extract normalizeLabels to internal/util/strings.go

- Created internal/util/strings.go with NormalizeLabels function
- Added comprehensive tests in internal/util/strings_test.go
- Updated internal/rpc/server_issues_epics.go to use util.NormalizeLabels
- Updated cmd/bd/list.go and cmd/bd/ready.go to use util.NormalizeLabels
- Updated cmd/bd/list_test.go to use util.NormalizeLabels
- Removed duplicate implementations
- All tests pass

Fixes bd-fb95094c.6

Amp-Thread-ID: https://ampcode.com/threads/T-edb3c286-cd60-4231-94cd-edaf75d84a3d
Co-authored-by: Amp <amp@ampcode.com>

cmd/bd/ready.go

@@ -9,6 +9,7 @@ import (
 	"github.com/steveyegge/beads/internal/rpc"
 	"github.com/steveyegge/beads/internal/storage/sqlite"
 	"github.com/steveyegge/beads/internal/types"
+	"github.com/steveyegge/beads/internal/util"
 )
 var readyCmd = &cobra.Command{
 	Use:   "ready",
@@ -22,8 +23,8 @@ var readyCmd = &cobra.Command{
 		// Use global jsonOutput set by PersistentPreRun (respects config.yaml + env vars)
 		
 		// Normalize labels: trim, dedupe, remove empty
-		labels = normalizeLabels(labels)
-		labelsAny = normalizeLabels(labelsAny)
+		labels = util.NormalizeLabels(labels)
+		labelsAny = util.NormalizeLabels(labelsAny)
 		
 		filter := types.WorkFilter{
 			// Leave Status empty to get both 'open' and 'in_progress' (bd-165)