Fix favicon (real icon, not an unrelated orange circle) + stack encouragements with the submit button

favicon.svg was a plain solid circle, unrelated to the actual brand
mark - replaced with the real single-arch icon (matching
infrastructure/assets/icon-{light,dark}.svg), split into two
prefers-color-scheme-scoped files rather than one SVG with an embedded
@media query - the latter doesn't reliably re-evaluate via <link> on
Safari/iOS (confirmed by prior real-device testing on the Gitea side,
see gitea-head.tmpl).

Encouragements used to render right after the description, separated
from the actual submit button by the whole features/requirements
block - moved them into the same wrapper as the form, directly above
the button, so reassurance text and the call to action read together.

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

style/main.css

@@ -178,6 +178,15 @@ main.loading, main.not-found {
   font-size: 0.9rem;
   color: var(--accent);
   font-style: italic;
+  margin: 0;
+}
+
+.alt-cta {
+  display: flex;
+  flex-direction: column;
+  align-items: flex-start;
+  gap: 0.4rem;
+  margin-top: 1.4rem;
 }
 
 .features { display: grid; gap: 1.1rem; margin-top: 0.6rem; }
@@ -272,7 +281,6 @@ input:focus, textarea:focus {
 .prosekit-editor p:last-child { margin-bottom: 0; }
 
 .alt-submit {
-  margin-top: 1.4rem;
   font-family: var(--sans);
   font-weight: 600;
   font-size: 0.95rem;