Hero becomes a content-owned module; site asset proxy; gesture growth fix

site.yaml's hero is now plain | module, where module names a
JavaScript file the content repo ships (mount(container) -> handle
with stop()). Portal serves content assets same-origin at
/site/<path> (Gitea raw sends no CORS headers), starts the module at
HTML parse time, adopts it on hydration, mounts fresh via the inline
script's __mountHero on client-side navigation, and stops it on
leave. The YES canvas (yes.js) and the gesture hero mode leave the
engine - uhhm/questions ships YES as its hero.js, redoal/questions
ships a sine-swings band. Gesture form canvas no longer balloons after
a stroke: the wrap's aspect-ratio reservation is scoped to :empty
(pre-mount) so it can't turn echo-strip height into width inside the
flex field.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

README.md

@@ -8,9 +8,12 @@ serves is declared in its content repo, and the same build serves any
 number of sites.
 
 Point an instance at a content repo and that repo *is* the site:
-pages, copy, state graphs, and branding (`site.yaml`: title,
-wordmark, and which hero the landing page opens on — the YES canvas,
-a gesture-drawing canvas wired to a relay, or plain copy). Content
+pages, copy, state graphs, branding, and even the landing hero
+(`site.yaml`: title, wordmark, and `hero: {kind: module, module:
+hero.js}` — a JavaScript module the content repo ships, served
+same-origin at `/site/<path>`, that portal mounts at parse time and
+stops on navigation; the YES canvas and redoal's sine swings are both
+content, not engine). Content
 pushes hot-reload every running instance; instances differ only by
 env vars. [uhhm.no](https://uhhm.no)
 ([uhhm/questions](https://project.uhhm.no/uhhm/questions)) and