fix(auth): login logo points at missing login-logo.png -> use logo.svg

templates/user/auth/signin_inner.tmpl referenced /assets/img/login-logo.png,
which is never shipped (404) — so the sign-in page rendered with no logo (the
onerror just hid it). Use the existing logo.svg (with a logo.png fallback and
alt text), matching templates/base/head_navbar.tmpl.

Note: the sign-in a11y/theme-toggle icons are NOT a code bug — Font Awesome 7 is
vendored (web_src/css/vendor/fontawesome) and @imported in index.css:6; they
render blank only on git.dev because that container runs the stale stable-395
image (pre-theme). Fixed by deploying current dev (see #816), not a template change.

Authored-by: Moko Consulting

templates/user/auth/signin_inner.tmpl

@@ -1,6 +1,7 @@
 <div class="ui container fluid">
 	<div class="tw-text-center tw-mb-4">
-		<img src="{{AssetUrlPrefix}}/img/login-logo.png" style="max-width: 220px; max-height: 80px; object-fit: contain;" onerror="this.style.display='none'">
+		<img src="{{AssetUrlPrefix}}/img/logo.svg" alt="{{ctx.Locale.Tr "logo"}}" style="max-width: 220px; max-height: 80px; object-fit: contain;" onerror="this.src='{{AssetUrlPrefix}}/img/logo.png'">
+
 	</div>
 	{{if or (not .LinkAccountMode) (and .LinkAccountMode .LinkAccountModeSignIn)}}
 	{{template "base/alert" .}}