feat(login): add language picker on the login page (#328)

The language selector previously lived only in Settings, which is
behind login. New users on a non-English system had no way to switch
to their language before connecting to a server.

Add a compact CustomSelect in the top-right of the login card. Reuses
the existing settings.languageXx labels and i18n.changeLanguage flow
(persists to localStorage as psysonic_language). English remains the
default for first launches — already the case in i18n.ts:12.

Styled to be visually quieter than the Settings variant (transparent
background, smaller font) so it doesn't pull focus from the logo and
form.

Co-authored-by: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/styles/components.css

@@ -4134,6 +4134,33 @@
   margin-bottom: var(--space-5);
 }
 
+.login-lang-picker {
+  position: absolute;
+  top: var(--space-3);
+  right: var(--space-3);
+  display: flex;
+  align-items: center;
+  gap: var(--space-1);
+  color: var(--text-muted);
+  z-index: 2;
+}
+
+.login-lang-picker > button {
+  font-size: 12px;
+  padding: 4px 8px;
+  background: transparent;
+  border: 1px solid transparent;
+  color: var(--text-muted);
+  width: auto;
+  min-width: 110px;
+}
+
+.login-lang-picker > button:hover {
+  background: var(--bg-hover);
+  border-color: var(--border-subtle);
+  color: var(--text-primary);
+}
+
 .login-title {
   text-align: center;
   font-family: var(--font-display);