Merge public ihasmail: the app's name comes from APP_NAME everywhere

Upstream's {app} placeholder (#406) replaces most of the fork's own
renamed strings: the user menu, the About heading and its version line
now say INBUXA because APP_NAME does, not because the fork wrote it in.

Kept from the fork: inbuxa.org rather than ihasmail.org, no Documentation
entry until INBUXA has its own, the INBUXA mark and wordmark, the "Built
on ihasmail" credit, and the About note that says nothing about the
server software. DEFAULT_APP_NAME stays INBUXA.

The credit's placeholder is {project} now, so the name of the project is
not spelled inside a key that upstream's new test reads as a hard-coded
app name.

web/src/views/AppShell.tsx

@@ -192,7 +192,7 @@ export function AppShell({ children }: { children: ReactNode }) {
                 app there was no way back to it.
                 ihasmail-inbuxa: INBUXA's site, and no Documentation entry until
                 INBUXA has documentation of its own to point at. */}
-            <MenuItem icon={<Globe size={16} />} label={t("About INBUXA")} href="https://inbuxa.org" external />
+            <MenuItem icon={<Globe size={16} />} label={t("About {app}", { app: appName })} href="https://inbuxa.org" external />
             <MenuItem icon={<Settings size={16} />} label={t("Settings")} onClick={() => navigate("/settings")} />
             {/* Only for an account whose Stalwart role manages other accounts.
                 Nobody else is shown an entry that would open onto refusals. */}