docs: add package comments to core infrastructure packages

internal/app/app.go

@@ -1,3 +1,4 @@
+// Package app bootstraps and wires the application dependencies.
 package app
 
 import (

internal/config/config.go

@@ -1,3 +1,4 @@
+// Package config provides application configuration loading and access.
 package config
 
 import (

internal/observability/log.go

@@ -1,3 +1,4 @@
+// Package observability provides logging and metrics instrumentation.
 package observability
 
 import (