ai-dev: graceful shutdown, tests, stdlib context, lint/CI, error logging

- T1: SIGTERM/SIGINT → client.Disconnect(250) → os.Exit(0)
- T2: 11 tests with miniredis mock (handleMessage, getEnv, parseInt, randomString)
- T3: golang.org/x/net/context → stdlib context, math/rand → math/rand/v2
- T4: .golangci.yml + .github/workflows/ci.yml
- T5: Redis SETEX error log includes key and memberID
- Dockerfile: add git for go mod tidy

.github/workflows/ci.yml

@@ -0,0 +1,38 @@
+name: CI
+
+on:
+  push:
+    branches: [main]
+  pull_request:
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.24"
+      - uses: golangci/golangci-lint-action@v6
+        with:
+          working-directory: mqtt_presence_redis_go
+
+  test:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.24"
+      - run: go test ./...
+        working-directory: mqtt_presence_redis_go
+
+  build:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: actions/setup-go@v5
+        with:
+          go-version: "1.24"
+      - run: go build ./...
+        working-directory: mqtt_presence_redis_go