Add unit tests and GitRepoSync e2e test

Add unit tests for all packages that previously had zero test coverage:
- pkg/apis/git/v1alpha1: defaults, deepcopy, scheme registration, constants
- pkg/client: toUnstructured/fromUnstructured round-trips, context injection
- pkg/reconciler/push: splitKey, nestedFieldNoCopy, unstructuredNestedStringMap, base64 decoding
- pkg/reconciler/sync: splitKey
- pkg/reconciler/resolver: splitKey, changeName

Add e2e test exercising the sync controller:
- Creates second Gitea repo and GitRepository CR
- Creates GitBranch CRs with headCommit set via status subresource patch
- Creates GitRepoSync CR and verifies the sync controller processes it

https://claude.ai/code/session_01QfFzqKQUsxxBsiZUhuJ3pG

pkg/apis/git/v1alpha1/defaults_test.go

@@ -0,0 +1,69 @@
+package v1alpha1
+
+import (
+	"testing"
+)
+
+func TestSetDefaults_GitRepository(t *testing.T) {
+	tests := []struct {
+		name           string
+		repo           *GitRepository
+		wantBranch     string
+	}{
+		{
+			name:       "empty default branch gets set to main",
+			repo:       &GitRepository{},
+			wantBranch: "main",
+		},
+		{
+			name: "explicit default branch is preserved",
+			repo: &GitRepository{
+				Spec: GitRepositorySpec{
+					DefaultBranch: "develop",
+				},
+			},
+			wantBranch: "develop",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			SetDefaults_GitRepository(tt.repo)
+			if got := tt.repo.Spec.DefaultBranch; got != tt.wantBranch {
+				t.Errorf("DefaultBranch = %q, want %q", got, tt.wantBranch)
+			}
+		})
+	}
+}
+
+func TestSetDefaults_GitPushTransaction(t *testing.T) {
+	tests := []struct {
+		name      string
+		txn       *GitPushTransaction
+		wantPhase TransactionPhase
+	}{
+		{
+			name:      "empty phase gets set to Pending",
+			txn:       &GitPushTransaction{},
+			wantPhase: TransactionPhasePending,
+		},
+		{
+			name: "existing phase is preserved",
+			txn: &GitPushTransaction{
+				Status: GitPushTransactionStatus{
+					Phase: TransactionPhaseSucceeded,
+				},
+			},
+			wantPhase: TransactionPhaseSucceeded,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			SetDefaults_GitPushTransaction(tt.txn)
+			if got := tt.txn.Status.Phase; got != tt.wantPhase {
+				t.Errorf("Phase = %q, want %q", got, tt.wantPhase)
+			}
+		})
+	}
+}