fix(oidc,ui): restore Authentik login and fix mobile delete dialog (#845)

OIDC: when OIDC_DISCOVERY_URL is explicitly set, trust the discovery
doc's issuer for id_token comparison instead of rejecting a path
mismatch as an error. Authentik (and similar realm-path providers)
return a canonical issuer like /application/o/<slug>/ that differs
from the operator's base OIDC_ISSUER. Strict equality blocked login
in 3.x despite working in v2. Default discovery (no custom URL) keeps
the strict check. Adds OIDC-SVC-037/038/039.

UI: ConfirmDialog and CopyTripDialog lacked the --bottom-nav-h
paddingBottom offset that other overlays already use. On mobile portrait
the action buttons were hidden behind the sticky bottom nav bar.

Closes #843
Closes #844

client/src/components/shared/ConfirmDialog.tsx

@@ -41,7 +41,7 @@ export default function ConfirmDialog({
   return (
     <div
       className="fixed inset-0 z-[10000] flex items-center justify-center px-4 trek-backdrop-enter"
-      style={{ backgroundColor: 'rgba(15, 23, 42, 0.5)' }}
+      style={{ backgroundColor: 'rgba(15, 23, 42, 0.5)', paddingBottom: 'var(--bottom-nav-h)' }}
       onClick={onClose}
     >
       <div

client/src/components/shared/CopyTripDialog.tsx

@@ -42,7 +42,7 @@ export default function CopyTripDialog({ isOpen, tripTitle, onClose, onConfirm }
   return (
     <div
       className="fixed inset-0 z-[10000] flex items-center justify-center px-4 trek-backdrop-enter"
-      style={{ backgroundColor: 'rgba(15, 23, 42, 0.5)' }}
+      style={{ backgroundColor: 'rgba(15, 23, 42, 0.5)', paddingBottom: 'var(--bottom-nav-h)' }}
       onClick={onClose}
     >
       <div