feat(ready): add --unassigned filter for bd ready

Add -u/--unassigned flag to bd ready command to show only issues
with no assignee. This supports the SCAVENGE protocol where polecats
query the 'Salvage Yard' for unassigned ready work.

Changes:
- Add NoAssignee field to WorkFilter struct
- Update SQLite GetReadyWork to filter by empty/null assignee
- Add --unassigned/-u flag to ready command
- Update RPC protocol and daemon handler
- Add test for NoAssignee filter functionality

Fixes: gt-3rp

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

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

cmd/bd/ready.go

@@ -39,7 +39,7 @@ var readyCmd = &cobra.Command{
 			priority, _ := cmd.Flags().GetInt("priority")
 			filter.Priority = &priority
 		}
-		if assignee != "" {
+		if assignee != "" && !unassigned {
 			filter.Assignee = &assignee
 		}
 		// Validate sort policy

cmd/bd/ready_test.go

@@ -260,3 +260,91 @@ func TestReadyCommandInit(t *testing.T) {
 		t.Error("readyCmd should have Short description")
 	}
 }
+
+func TestReadyWorkUnassigned(t *testing.T) {
+	tmpDir := t.TempDir()
+	testDB := filepath.Join(tmpDir, ".beads", "beads.db")
+	s := newTestStore(t, testDB)
+	ctx := context.Background()
+
+	// Create issues with different assignees
+	issues := []*types.Issue{
+		{
+			ID:        "test-unassigned-1",
+			Title:     "Unassigned task 1",
+			Status:    types.StatusOpen,
+			Priority:  1,
+			IssueType: types.TypeTask,
+			Assignee:  "",
+			CreatedAt: time.Now(),
+		},
+		{
+			ID:        "test-unassigned-2",
+			Title:     "Unassigned task 2",
+			Status:    types.StatusOpen,
+			Priority:  2,
+			IssueType: types.TypeTask,
+			CreatedAt: time.Now(),
+		},
+		{
+			ID:        "test-assigned-alice",
+			Title:     "Alice's task",
+			Status:    types.StatusOpen,
+			Priority:  1,
+			IssueType: types.TypeTask,
+			Assignee:  "alice",
+			CreatedAt: time.Now(),
+		},
+		{
+			ID:        "test-assigned-bob",
+			Title:     "Bob's task",
+			Status:    types.StatusOpen,
+			Priority:  1,
+			IssueType: types.TypeTask,
+			Assignee:  "bob",
+			CreatedAt: time.Now(),
+		},
+	}
+
+	for _, issue := range issues {
+		if err := s.CreateIssue(ctx, issue, "test"); err != nil {
+			t.Fatal(err)
+		}
+	}
+
+	// Test filtering by --unassigned
+	readyUnassigned, err := s.GetReadyWork(ctx, types.WorkFilter{
+		Unassigned: true,
+	})
+	if err != nil {
+		t.Fatalf("GetReadyWork with Unassigned filter failed: %v", err)
+	}
+
+	// Should only have unassigned issues
+	if len(readyUnassigned) != 2 {
+		t.Errorf("Expected 2 unassigned issues, got %d", len(readyUnassigned))
+	}
+
+	for _, issue := range readyUnassigned {
+		if issue.Assignee != "" {
+			t.Errorf("Expected no assignee, got %q for issue %s", issue.Assignee, issue.ID)
+		}
+	}
+
+	// Test that Unassigned takes precedence over Assignee filter
+	alice := "alice"
+	readyConflict, err := s.GetReadyWork(ctx, types.WorkFilter{
+		Unassigned: true,
+		Assignee:   &alice,
+	})
+	if err != nil {
+		t.Fatalf("GetReadyWork with conflicting filters failed: %v", err)
+	}
+
+	// Unassigned should win, returning only unassigned issues
+	for _, issue := range readyConflict {
+		if issue.Assignee != "" {
+			t.Errorf("Unassigned should override Assignee filter, got %q for issue %s", issue.Assignee, issue.ID)
+		}
+	}
+}