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/reconciler/sync/sync_test.go

@@ -0,0 +1,54 @@
+package sync
+
+import (
+	"testing"
+)
+
+func TestSplitKey(t *testing.T) {
+	tests := []struct {
+		key      string
+		wantNS   string
+		wantName string
+	}{
+		{
+			key:      "default/my-sync",
+			wantNS:   "default",
+			wantName: "my-sync",
+		},
+		{
+			key:      "git-system/sync-controller",
+			wantNS:   "git-system",
+			wantName: "sync-controller",
+		},
+		{
+			key:      "just-name",
+			wantNS:   "",
+			wantName: "just-name",
+		},
+		{
+			key:      "",
+			wantNS:   "",
+			wantName: "",
+		},
+		{
+			key:      "ns/name/extra",
+			wantNS:   "ns",
+			wantName: "name/extra",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.key, func(t *testing.T) {
+			ns, name, err := splitKey(tt.key)
+			if err != nil {
+				t.Fatalf("splitKey(%q) error = %v", tt.key, err)
+			}
+			if ns != tt.wantNS {
+				t.Errorf("namespace = %q, want %q", ns, tt.wantNS)
+			}
+			if name != tt.wantName {
+				t.Errorf("name = %q, want %q", name, tt.wantName)
+			}
+		})
+	}
+}