Implement auto-routing for bd create (bd-ubu2)

- Add internal/routing package with DetectUserRole and DetermineTargetRepo
- Add routing config schema (mode, default, maintainer, contributor)
- Add --repo flag to bd create for explicit override
- Integrate routing logic into create command
- Test with contributor/maintainer roles and explicit override

Part of bd-8hf (Auto-routing and maintainer detection)

internal/routing/routing_test.go

@@ -0,0 +1,90 @@
+package routing
+
+import (
+	"testing"
+)
+
+func TestDetermineTargetRepo(t *testing.T) {
+	tests := []struct {
+		name     string
+		config   *RoutingConfig
+		userRole UserRole
+		repoPath string
+		want     string
+	}{
+		{
+			name: "explicit override takes precedence",
+			config: &RoutingConfig{
+				Mode:                "auto",
+				DefaultRepo:         "~/planning",
+				MaintainerRepo:      ".",
+				ContributorRepo:     "~/contributor-planning",
+				ExplicitOverride:    "/tmp/custom",
+			},
+			userRole: Maintainer,
+			repoPath: ".",
+			want:     "/tmp/custom",
+		},
+		{
+			name: "auto mode - maintainer uses maintainer repo",
+			config: &RoutingConfig{
+				Mode:            "auto",
+				MaintainerRepo:  ".",
+				ContributorRepo: "~/contributor-planning",
+			},
+			userRole: Maintainer,
+			repoPath: ".",
+			want:     ".",
+		},
+		{
+			name: "auto mode - contributor uses contributor repo",
+			config: &RoutingConfig{
+				Mode:            "auto",
+				MaintainerRepo:  ".",
+				ContributorRepo: "~/contributor-planning",
+			},
+			userRole: Contributor,
+			repoPath: ".",
+			want:     "~/contributor-planning",
+		},
+		{
+			name: "explicit mode uses default",
+			config: &RoutingConfig{
+				Mode:        "explicit",
+				DefaultRepo: "~/planning",
+			},
+			userRole: Maintainer,
+			repoPath: ".",
+			want:     "~/planning",
+		},
+		{
+			name: "no config defaults to current directory",
+			config: &RoutingConfig{
+				Mode: "auto",
+			},
+			userRole: Maintainer,
+			repoPath: ".",
+			want:     ".",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			got := DetermineTargetRepo(tt.config, tt.userRole, tt.repoPath)
+			if got != tt.want {
+				t.Errorf("DetermineTargetRepo() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}
+
+func TestDetectUserRole_Fallback(t *testing.T) {
+	// Test fallback behavior when git is not available
+	role, err := DetectUserRole("/nonexistent/path/that/does/not/exist")
+	if err != nil {
+		t.Fatalf("DetectUserRole() error = %v, want nil", err)
+	}
+	if role != Contributor {
+		t.Errorf("DetectUserRole() = %v, want %v (fallback)", role, Contributor)
+	}
+}