Convert toast.js to TypeScript (issue #17)

- Add ts/toast.ts: typed port of the Alpine toast store + window.toast +
  window.fetchWithHtmxTriggers. Toast / ToastStore / ToastMessage interfaces
  type the store and the show-toast CustomEvent detail; Alpine declared as a
  type-only ambient global
- Declare window.toast in ts/globals.d.ts
- Stays a classic (non-module) script — no import/export — so it keeps defining
  globals; layout.py now serves dist/toast.js

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

common/layout.py

@@ -364,7 +364,7 @@ def Page(
         "        <!-- hx-swap-oob makes sure the modal gets removed upon any HTMX response -->\n"
         '        <div id="global-modal-container" hx-swap-oob="true"></div>\n'
         f"        {_TOAST_CONTAINER}\n"
-        f'        <script src="{static("js/toast.js")}"></script>\n'
+        f'        <script src="{static("js/dist/toast.js")}"></script>\n'
         "    </body>\n</html>\n"
     )