chore(dev): run backend with air

backend/.air.toml

@@ -0,0 +1,30 @@
+root = "."
+tmp_dir = "tmp"
+
+[build]
+cmd = "go build -o ./tmp/aethera ./cmd"
+bin = "./tmp/aethera"
+full_bin = "./tmp/aethera --listen 0.0.0.0"
+delay = 1000
+exclude_dir = ["data", "dist", "tmp", "web/static"]
+exclude_file = []
+exclude_regex = ["_test.go"]
+include_dir = []
+include_ext = ["go", "mod", "sum"]
+kill_delay = "500ms"
+log = "build-errors.log"
+send_interrupt = true
+stop_on_error = true
+
+[color]
+app = ""
+build = "yellow"
+main = "magenta"
+runner = "green"
+watcher = "cyan"
+
+[log]
+time = false
+
+[misc]
+clean_on_exit = true

backend/AGENTS.md

@@ -3,6 +3,7 @@
 ## Stack
 
 - **Go 1.25.5** (`reichard.io/aethera`)
+- **air** (backend hot reload for `make dev`)
 - **cobra** (CLI framework)
 - **logrus** (structured logging)
 - **openai-go/v3** (OpenAI API client)