Implement Git-as-K8s control plane with Knative controllers

Build a complete Kubernetes control plane for Git operations using Knative's
pkg framework, go-git for in-memory Git operations, and ko for builds.

Architecture:
- 4 CRDs: GitRepository, GitBranch, GitPushTransaction, GitRepoSync
- Push controller: atomic Git push via go-git with CAS (compare-and-swap)
- Sync controller: two-way sync with in-memory merge base calculation
- Resolver controller: automated 3-way merge for conflicted syncs
- In-cluster Gitea server for backing storage
- Full RBAC, ko-based deployments, and code-gen scaffolding

Note: go.sum needs generation via `go mod tidy` in an environment with
full internet access (knative.dev/pkg v0.0.0-20250520014526-44579e9ce5ed).

https://claude.ai/code/session_01QfFzqKQUsxxBsiZUhuJ3pG

cmd/push-controller/main.go

@@ -0,0 +1,11 @@
+package main
+
+import (
+	"knative.dev/pkg/injection/sharedmain"
+
+	"github.com/imjasonh/git-k8s/pkg/reconciler/push"
+)
+
+func main() {
+	sharedmain.Main("push-controller", push.NewController)
+}