feat: extract kafkamgmt.v1 proto contract from kafaka_management_service

Single source of truth for the wire contract shared by the server,
kmsvc-sdk, and kmsvc-cli. Ships proto source + buf lint/breaking-change
config only; consumers submodule this repo and codegen independently
with their own go_package override (see README.md).

README.md

@@ -0,0 +1,32 @@
+# kmsvc-proto
+
+Shared `kafkamgmt.v1` proto contract for the Kafka Management Service ecosystem (`kafaka_management_service`, `kmsvc-sdk`, `kmsvc-cli`).
+
+This repo ships **`.proto` source + buf lint/breaking-change config only** — no generated code. Each consumer submodules this repo and runs its own `buf generate` with its own pinned plugin versions and `go_package` override (managed mode), so generated-runtime versions never need to match across repos — only the wire contract is shared.
+
+## Consuming this repo
+
+```bash
+git submodule add https://forgejo.riotpiao.homelab.com/rock/kmsvc-proto.git proto
+git -C proto checkout v1.0.0   # pin to a tag, don't track a moving branch
+```
+
+Then point your own `buf.gen.yaml` at `proto/proto` (this repo's proto root) and use managed mode to set your module's own `go_package`:
+
+```yaml
+version: v2
+managed:
+  enabled: true
+  override:
+    - file_option: go_package
+      value: github.com/<you>/<your-module>/internal/genapi
+plugins:
+  - local: protoc-gen-go
+    out: internal/genapi
+    opt: paths=source_relative
+  - local: protoc-gen-go-grpc
+    out: internal/genapi
+    opt: paths=source_relative
+```
+
+See `PLAN.md` for the full rollout plan (tagging convention, server migration, SDK/CLI wiring).