Scaffold project with Kubebuilder v4

kubebuilder init --domain ryuvia.com --repo git.ryuvia.com/niklas/terdut-operator
(--license none, no per-file header boilerplate -- terdut-server's source carries
none either). Go 1.26.0/controller-runtime v0.25.0/controller-tools v0.22.0, whatever
the current kubebuilder CLI (v4.16.0) scaffolds -- not pinned back to terdut-server's
go 1.25.9, since this is a separate module with its own toolchain.

Verified locally: build, vet, fmt all clean; `make lint` (golangci-lint, fetched into
bin/) 0 issues; `make test` (controller-gen + setup-envtest, fetched into bin/,
downloads real envtest binaries from storage.googleapis.com) passes.

Dropped kubebuilder's default .github/workflows/* -- this org runs on Gitea, not
GitHub; ci.yaml (next commit) is the only CI this repo gets.

.devcontainer/devcontainer.json

@@ -0,0 +1,35 @@
+{
+  "name": "Kubebuilder DevContainer",
+  "image": "golang:1.26",
+  "features": {
+    "ghcr.io/devcontainers/features/docker-in-docker:2": {
+      "moby": false,
+      "dockerDefaultAddressPool": "base=172.30.0.0/16,size=24"
+    },
+    "ghcr.io/devcontainers/features/git:1": {},
+    "ghcr.io/devcontainers/features/common-utils:2": {
+      "upgradePackages": true
+    }
+  },
+
+  "runArgs": ["--privileged", "--init"],
+
+  "customizations": {
+    "vscode": {
+      "settings": {
+        "terminal.integrated.shell.linux": "/bin/bash"
+      },
+      "extensions": [
+        "ms-kubernetes-tools.vscode-kubernetes-tools",
+        "ms-azuretools.vscode-docker"
+      ]
+    }
+  },
+
+  "remoteEnv": {
+    "GO111MODULE": "on"
+  },
+
+  "onCreateCommand": "bash .devcontainer/post-install.sh"
+}
+