feat: add Air hot reload config for backend development

backend/.air.toml

@@ -0,0 +1,15 @@
+root = "."
+tmp_dir = "tmp"
+
+[build]
+  cmd = "go build -o ./tmp/base.exe base.go"
+  bin = "./tmp/base.exe -f etc/base-api.yaml"
+  include_ext = ["go", "yaml"]
+  exclude_dir = ["tmp", "vendor", "tests"]
+  delay = 1000
+
+[log]
+  time = false
+
+[misc]
+  clean_on_exit = true

backend/.gitignore

@@ -0,0 +1 @@
+tmp/