chore(infra): add gRPC layer, update protobufs, remove immediate module

- Add gRPC service modules: auth, channel, channel settings, member,
  permission
- Update protobuf definitions and generated code
- Remove immediate/ real-time module (superseded by IM service)
- Update etcd discovery and registration
- Update cache, error, config, and build infrastructure
- Add ADR documentation
- Update OpenAPI spec

docs/adr/000-adr-template.md

@@ -0,0 +1,50 @@
+# ADR-NNN: 标题 / Title
+
+## 状态 / Status
+
+**Accepted** | Superseded | Deprecated
+
+**日期 / Date**: YYYY-MM-DD
+
+## 背景 / Context
+
+描述问题背景和驱动因素。
+
+Describe the context and driving factors.
+
+## 决策 / Decision
+
+描述做出的决策。
+
+Describe the decision that was made.
+
+## 考虑的方案 / Considered Options
+
+1. **方案 A** — 描述 / Description
+2. **方案 B** — 描述 / Description
+3. **方案 C** — 描述 / Description
+
+## 后果 / Consequences
+
+### 正面 / Positive
+
+- 优点 1 / Advantage 1
+- 优点 2 / Advantage 2
+
+### 负面 / Negative
+
+- 缺点 1 / Disadvantage 1
+- 缺点 2 / Disadvantage 2
+
+### 风险 / Risks
+
+- 风险 1 / Risk 1
+- 风险 2 / Risk 2
+
+## 相关决策 / Related Decisions
+
+- [ADR-XXX](xxx-related-decision.md)
+
+## 参考 / References
+
+- [链接 / Link](url)