docs: add doc.go and expand README for V1

Document lifecycle concepts, companion packages, and API reference.
Add gitignore for coverage artifacts.

Co-authored-by: Cursor <cursoragent@cursor.com>

doc.go

@@ -0,0 +1,26 @@
+// Package app orchestrates modular application setup and teardown.
+//
+// Register subsystems as [Module] values, attach them to a [Lifecycle], and call
+// [Lifecycle.Setup] or [Lifecycle.Require] to initialize resources in dependency
+// order. Always call [Lifecycle.Teardown] (typically via defer) to release
+// resources in reverse setup order.
+//
+// Module authors (dbx, applog, migrate, etc.) and main/cmd packages both import
+// app. Use [Lifecycle.Context] to propagate the lifecycle through context.Context
+// for CLI commands via [gitea.auvem.com/go-toolkit/appcli].
+//
+// # Concepts
+//
+//   - [Module] — named unit with optional Setup, Teardown, and Depends
+//   - [Lifecycle] — registry and orchestrator for modules
+//   - Setup order — dependencies first; autoload resolves Depends when enabled
+//   - Require — lazy/conditional setup (common in CLI subcommands)
+//
+// # API overview
+//
+// Lifecycle — [NewLifecycle], [Lifecycle.Setup], [Lifecycle.Teardown],
+// [Lifecycle.Require], [Lifecycle.RequireWithOpts], [Lifecycle.GetModule],
+// [Lifecycle.Context], [LifecycleFromContext]
+//
+// Module — [NewModule], [Module.Lifecycle], [Module.Logger], [Module.Loaded]
+package app