feat: k8s informer for ServiceAdapter CRDs, bump CI to go1.26

- Add dynamic-client informer to watch ServiceAdapter CRs in-cluster
- Remove typed scheme registration (dynamic client needs no DeepCopy)
- Bump Dockerfile + CI images from golang:1.25 to golang:1.26
  (k8s.io/[email protected] requires go>=1.26)
- Wire informer into main.go startup with graceful fallback

.gitea/workflows/build.yaml

@@ -18,7 +18,7 @@ jobs:
     # golang, not a retired generic "docker" runner -- this repo is Go, and
     # every runner now carries its own dind sidecar to build/push that
     # repo's images. `container.image` below overrides the runner's own
-    # default (golang:1.25-bookworm) with docker:27-cli for this job only.
+    # default (golang:1.26-bookworm) with docker:27-cli for this job only.
     runs-on: golang
     container:
       image: docker:27-cli

.gitea/workflows/ci.yaml

@@ -27,10 +27,10 @@ jobs:
     name: Test, vet, build
     runs-on: golang
     container:
-      image: golang:1.25-bookworm
+      image: golang:1.26-bookworm
     steps:
       # actions/checkout@v4 is a JS action -- Forgejo Actions execs it with
-      # `node`, which golang:1.25-bookworm doesn't ship. Without this the
+      # `node`, which golang:1.26-bookworm doesn't ship. Without this the
       # checkout step fails with "exec: node: executable file not found in
       # $PATH" before any of the job's own steps run. Same fix already in use
       # in kmsvc-manage's ci.yaml; carried over here.