Comprehensive review fixes: security, performance, code quality, and UI polish

Backend: Fix CORS wildcard+credentials, add secret key warning, remove raw
API keys from sync endpoint, fix N+1 queries in watcher/sync, fix
AttributeError on event_types, delete dead scheduled.py/templates.py,
add limit cap on history, re-validate server on URL/key update, apply
tracking/template config IDs in update_target.

HA Integration: Replace datetime.now() with dt_util.now(), fix notification
queue to only remove successfully sent items, use album UUID for entity
unique IDs, add shared links dirty flag and users cache hourly refresh,
deduplicate _is_quiet_hours, add HTTP timeouts, cache albums in config
flow, change iot_class to local_polling.

Frontend: Make i18n reactive via $state (remove window.location.reload),
add Modal transitions/a11y/Escape key, create ConfirmModal replacing all
confirm() calls, add error handling to all pages, replace Unicode nav
icons with MDI SVGs, add card hover effects, dashboard stat icons, global
focus-visible styles, form slide transitions, mobile responsive bottom
nav, fix password error color, add ~20 i18n keys (EN/RU).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/lib/components/ConfirmModal.svelte

@@ -0,0 +1,26 @@
+<script lang="ts">
+	import Modal from './Modal.svelte';
+	import { t } from '$lib/i18n';
+
+	let { open = false, title = '', message = '', onconfirm, oncancel } = $props<{
+		open: boolean;
+		title?: string;
+		message?: string;
+		onconfirm: () => void;
+		oncancel: () => void;
+	}>();
+</script>
+
+<Modal {open} title={title || t('common.confirm')} onclose={oncancel}>
+	<p class="text-sm text-[var(--color-muted-foreground)] mb-4">{message}</p>
+	<div class="flex gap-2 justify-end">
+		<button onclick={oncancel}
+			class="px-3 py-1.5 rounded-md text-sm border border-[var(--color-border)] hover:bg-[var(--color-muted)] transition-colors">
+			{t('common.cancel')}
+		</button>
+		<button onclick={onconfirm}
+			class="px-3 py-1.5 rounded-md text-sm bg-[var(--color-destructive)] text-white hover:opacity-90 transition-opacity">
+			{t('common.delete')}
+		</button>
+	</div>
+</Modal>