feat(01-02): create Docker Compose dev environment with hot reload

- docker-compose.yml orchestrates backend service with Air
- Bind mount for live code editing with cached consistency
- Named volume for persistent /data storage
- .air.toml configures Go hot reload on file changes
- Targets builder stage from multi-stage Dockerfile

.air.toml

@@ -0,0 +1,44 @@
+root = "."
+testdata_dir = "testdata"
+tmp_dir = "tmp"
+
+[build]
+  args_bin = []
+  bin = "./tmp/server"
+  cmd = "go build -o ./tmp/server ./cmd/server"
+  delay = 1000
+  exclude_dir = ["assets", "tmp", "vendor", ".planning", "docker", ".git"]
+  exclude_file = []
+  exclude_regex = ["_test.go"]
+  exclude_unchanged = false
+  follow_symlink = false
+  full_bin = ""
+  include_dir = []
+  include_ext = ["go", "tpl", "tmpl", "html"]
+  include_file = []
+  kill_delay = "0s"
+  log = "build-errors.log"
+  poll = false
+  poll_interval = 0
+  rerun = false
+  rerun_delay = 500
+  send_interrupt = false
+  stop_on_error = false
+
+[color]
+  app = ""
+  build = "yellow"
+  main = "magenta"
+  runner = "green"
+  watcher = "cyan"
+
+[log]
+  main_only = false
+  time = false
+
+[misc]
+  clean_on_exit = false
+
+[screen]
+  clear_on_rebuild = false
+  keep_scroll = true

docker-compose.yml

@@ -0,0 +1,18 @@
+services:
+  backend:
+    build:
+      context: .
+      dockerfile: docker/Dockerfile
+      target: builder  # Stop at build stage for dev
+    command: air -c .air.toml
+    ports:
+      - "32768:32768"
+    volumes:
+      - .:/workspace:cached  # Bind mount for live editing
+      - data:/data           # Named volume for persistent data
+    working_dir: /workspace
+    environment:
+      - CGO_ENABLED=0
+
+volumes:
+  data: