feat(studio): deploy manual designer and configurable AI model

README.md

@@ -117,7 +117,7 @@ APIMART_API_KEY=your_apimart_key
 
 Restart the app after setting the key. No key goes in the browser or application
 configuration. The server calls https://api.apimart.ai/v1/chat/completions with
-model `gpt-6-luna`, bearer authentication, and `stream: false`, as described in
+model `gpt-5-mini`, bearer authentication, and `stream: false`, as described in
 https://docs.apimart.ai/en/api-reference/texts/general/chat-completions.
 Model access must be available on your APIMart account. No live provider call is
 part of the normal build or test suite.
@@ -191,3 +191,6 @@ component gallery page.
 ### Interactive Studio gallery
 
 Choose Component gallery in the preview Content menu, then select pages 1–7. Each of the 104 entries has populated sample data and local icons. Controls use their shipped browser functions; charts and workflow graphs include their real runtimes. Sample events appear below each example. Preview links stay in the demo; forms and uploads do not submit data. Switch tracks stay rounded across presets and existing drafts. The editor reports when the preview is rendering, ready or unable to load.
+
+Manual design works without an API key: choose a preset or Create new, edit light/dark colors, fonts, corner radii, spacing and shadows, select Update preview, then export under Review & apply. Undo and decision locks protect changes.
+Set `APIMART_MODEL=gpt-5-mini` in the server `.env` to choose the AI model. Restart the server after changing it; the Studio displays the active model.