fix: frontend UX improvements (SSE status, responsive tables, dark mode, login toggle, theme)

- Add SSE connection status banner showing when real-time updates are lost (UX-H8, UX-M1)
- Add password visibility toggle on login page (UX-H10)
- Add dark mode variants to stat card backgrounds (UX-M11)
- Add overflow-x-auto to tables for mobile responsiveness (UX-H9)
- Add flex-wrap to stage header for mobile overflow (UX-H11)
- Fix theme store system preference listener reactivity (UX-M12)
- Parallelize registry health checks (UX-L4)

web/src/routes/projects/[id]/env/+page.svelte

@@ -192,7 +192,7 @@
 			{#if Object.keys(projectEnv).length > 0}
 				<div>
 					<h2 class="text-sm font-semibold text-[var(--text-secondary)]">{$t('envEditor.projectDefaults')}</h2>
-					<div class="mt-2 overflow-hidden rounded-xl border border-[var(--border-primary)] bg-[var(--surface-card-hover)]">
+					<div class="mt-2 overflow-x-auto rounded-xl border border-[var(--border-primary)] bg-[var(--surface-card-hover)]">
 						<table class="min-w-full divide-y divide-[var(--border-primary)]">
 							<thead>
 								<tr>
@@ -231,7 +231,7 @@
 						<span class="text-sm">{$t('common.loading')}</span>
 					</div>
 				{:else}
-					<div class="mt-2 overflow-hidden rounded-xl border border-[var(--border-primary)] bg-[var(--surface-card)] shadow-[var(--shadow-sm)]">
+					<div class="mt-2 overflow-x-auto rounded-xl border border-[var(--border-primary)] bg-[var(--surface-card)] shadow-[var(--shadow-sm)]">
 						<table class="min-w-full divide-y divide-[var(--border-primary)]">
 							<thead class="bg-[var(--surface-card-hover)]">
 								<tr>