feat(start): show paying Patreon supporters on the Start page

Add a right-hand rail on the Start page listing active paying patrons
(name + pledge amount, highest first) with a "Support on Patreon" button.
The list is fetched once at boot from the Patreon API in the background;
free followers, $0 tiers, declined and former patrons are excluded.

The creator access token is read at build time from OCS_PATREON_TOKEN
(option_env!), so it never lives in source or git — the release workflow
passes it from a repo secret, and build.rs re-bakes when it changes.
Without a token the rail just shows the support button.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/update/mod.rs

@@ -2592,6 +2592,13 @@ impl OpenCADStudio {
                 self.marketplace_status = format!("Registry: {e}");
                 Task::none()
             }
+            Message::PatronsFetched(Ok(names)) => {
+                self.patrons = names;
+                Task::none()
+            }
+            // No token / offline: leave the list empty (Start page shows a
+            // "Support on Patreon" prompt instead).
+            Message::PatronsFetched(Err(_)) => Task::none(),
             Message::PluginReleasesFetched(repo, Ok(tags)) => {
                 if let Some(first) = tags.first() {
                     self.repo_selected_tag