refactor(nav): Today tab shortcut to week view; delete /today route

- Today nav link targets /week?week=<currentWeek>&day=<todayKey>
- Today tab active: route=/week AND ?day===todayKey() (not just pathname)
- Week tab active: route=/week AND today tab not active
- Root / redirect updated from /today to /week?week=…&day=…
- /today route hard-deleted (src/routes/today/ removed)
- +layout.svelte imports todayKey/currentWeekKey for link generation

web/src/routes/+layout.svelte

@@ -4,6 +4,7 @@
 	import { onMount, onDestroy } from 'svelte';
 	import { goto } from '$app/navigation';
 	import { startSync, stopSync } from '$lib/stores/sync';
+	import { todayKey, currentWeekKey } from '$lib/utils';
 
 	let { children } = $props();
 
@@ -16,18 +17,26 @@
 
 	onDestroy(stopSync);
 
-	const navItems = [
-		{ href: '/today', label: 'Today' },
-		{ href: '/week', label: 'Week' },
-		{ href: '/history', label: 'History' },
-		{ href: '/settings', label: 'Settings' }
-	];
+	function todayHref(): string {
+		return `/week?week=${currentWeekKey()}&day=${todayKey()}`;
+	}
+
+	// "Today" tab is active when on /week with ?day === todayKey().
+	const todayActive = $derived(
+		page.url.pathname === '/week' &&
+		page.url.searchParams.get('day') === todayKey()
+	);
+
+	const weekActive = $derived(
+		page.url.pathname === '/week' && !todayActive
+	);
 </script>
 
 <nav>
-	{#each navItems as item}
-		<a href={item.href} class:active={page.url.pathname === item.href}>{item.label}</a>
-	{/each}
+	<a href={todayHref()} class:active={todayActive}>Today</a>
+	<a href="/week" class:active={weekActive}>Week</a>
+	<a href="/history" class:active={page.url.pathname === '/history'}>History</a>
+	<a href="/settings" class:active={page.url.pathname === '/settings'}>Settings</a>
 </nav>
 
 <main>

web/src/routes/+page.svelte

@@ -1,5 +1,6 @@
 <script lang="ts">
 	import { goto } from '$app/navigation';
 	import { onMount } from 'svelte';
-	onMount(() => goto('/today'));
+	import { todayKey, currentWeekKey } from '$lib/utils';
+	onMount(() => goto(`/week?week=${currentWeekKey()}&day=${todayKey()}`));
 </script>

web/src/routes/today/+page.svelte

@@ -1,19 +0,0 @@
-<script lang="ts">
-	import DayDetail from '$lib/components/DayDetail.svelte';
-	import { todayKey, dayCapabilities } from '$lib/utils';
-
-	const today = todayKey();
-	// Today is always open on mount; DayDetail will discover closed state from API.
-	// We pass a conservative open-today capabilities set; DayDetail adapts once loaded.
-	const capabilities = dayCapabilities(today, today, false);
-</script>
-
-<div class="today-page">
-	<h1>Today — {today}</h1>
-	<DayDetail dayKey={today} {capabilities} />
-</div>
-
-<style>
-	.today-page { padding: 0; }
-	h1 { margin: 0 0 1rem; font-size: 1.4rem; }
-</style>