refactor: move TodoMVC example into example/ directory

- example/todomvc/pocketbook/todomvc.cljs — app source
- example/todomvc/todomvc.html — page
- example/todomvc/js/ — compiled output (gitignored)

Server static file serving is now filesystem-based via --static-dir
flag instead of classpath resources. No static dir by default (API
only); bb server passes --static-dir example/todomvc.

Removed resources/public/ — library has no bundled static assets.

build.edn

@@ -1,5 +1,5 @@
 {:main       pocketbook.todomvc
- :output-to  "resources/public/js/main.js"
- :output-dir "resources/public/js/out"
+ :output-to  "example/todomvc/js/main.js"
+ :output-dir "example/todomvc/js/out"
  :asset-path "js/out"
  :optimizations :none}