Support public dir (#4783)

* Add optional static_dir support

- add optional application.static_dir field defaulting to none
- copy configured static directory into web output during build/serve
- document config knob and add unit tests
- force full rebuild when static_dir contents change
- sync removes stale outputs and logs copy activity
- track static manifest next to platform dir

Tests: cargo fmt

* default to public dir to match vite

* static_dir -> public_dir

* wip

* deser as none...

* wip... use .manifest.json

* implement dumb form of asset manifest generation

* implement manifest using asset system directly

* cleanup

* dont create extra asset dir for server

---------

Co-authored-by: Evan Almloff <evanalmloff@gmail.com>
Co-authored-by: Jonathan Kelley <jkelleyrtp@gmail.com>

packages/cli/README.md

@@ -60,9 +60,11 @@ name = "project-name"
 # Currently supported platforms: web, desktop
 default_platform = "web"
 
+# Optional: enable copying from a static directory (e.g. "public")
+public_dir = "public"
+
 [web.app]
 title = "Hello"
 
 [web.resource.dev]
 ```
-