Add week view to web calendar with Month/Week toggle

Extract the shared per-calendar event-collection logic out of
buildMonthView into collectCalendarEvents, keyed by day so it can feed
either the existing 42-cell month grid or a new 7-cell week grid.

Add templates.WeekDay/WeekViewData, a WeekView templ, and a
viewSwitcher component shown in both views' headers to switch between
Month and Week. Add buildWeekView, handleCalendarWeek, parseWeekStart,
and mondayOf in internal/web/calendar.go, and register the new
/calendar/week route.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

internal/web/templates/calendar.templ

@@ -50,8 +50,33 @@ type MonthViewData struct {
 	PrevMonthURL string
 	NextMonthURL string
 	TodayURL     string
+	WeekURL      string // link to switch to the week view
 }
 
+// WeekDay is one day column in the week grid.
+type WeekDay struct {
+	Date    string // "YYYY-MM-DD", used for links and the "new event" date
+	Weekday string // full weekday name, e.g. "Monday"
+	Day     int    // day-of-month number shown in the column header
+	Month   string // short month abbreviation, e.g. "Aug" (for cross-month weeks)
+	IsToday bool
+	Events  []EventSummary
+}
+
+// WeekViewData is everything the week grid template needs to render one
+// 7-day week across every calendar (own + shared) visible to the viewer.
+type WeekViewData struct {
+	Calendars   []CalendarSummary
+	HasWritable bool
+	RangeLabel  string // e.g. "Aug 18 – 24, 2026"
+	Days        []WeekDay
+	PrevWeekURL string
+	NextWeekURL string
+	TodayURL    string
+	MonthURL    string // link to switch to the month view
+}
+
+
 // CalendarOption is one entry in the "new event" calendar <select>.
 type CalendarOption struct {
 	Ref   string
@@ -84,6 +109,7 @@ templ MonthView(username string, data MonthViewData) {
 				<a href={ templ.URL(data.TodayURL) } class="bg-white border border-gray-300 rounded-md px-3 py-1.5 text-sm font-medium text-gray-700 hover:bg-gray-50">Today</a>
 				<a href={ templ.URL(data.NextMonthURL) } class="bg-white border border-gray-300 rounded-md px-3 py-1.5 text-sm font-medium text-gray-700 hover:bg-gray-50">&rarr;</a>
 				<span class="text-lg font-medium ml-2">{ data.MonthLabel }</span>
+				@viewSwitcher("month", "/web/calendar", data.WeekURL)
 				if data.HasWritable {
 					<a href="/web/calendar/new"
 						class="bg-indigo-600 text-white rounded-md px-3 py-1.5 text-sm font-medium hover:bg-indigo-700 ml-2">
@@ -119,6 +145,26 @@ templ MonthView(username string, data MonthViewData) {
 	}
 }
 
+// viewSwitcher renders the Month/Week toggle shown in both views'
+// headers. active is "month" or "week"; monthURL/weekURL are the
+// destinations for switching to each view.
+templ viewSwitcher(active, monthURL, weekURL string) {
+	<div class="inline-flex rounded-md border border-gray-300 overflow-hidden ml-2">
+		<a
+			href={ templ.URL(monthURL) }
+			class={ "px-3 py-1.5 text-sm font-medium", templ.KV("bg-indigo-600 text-white", active == "month"), templ.KV("bg-white text-gray-700 hover:bg-gray-50", active != "month") }
+		>
+			Month
+		</a>
+		<a
+			href={ templ.URL(weekURL) }
+			class={ "px-3 py-1.5 text-sm font-medium border-l border-gray-300", templ.KV("bg-indigo-600 text-white", active == "week"), templ.KV("bg-white text-gray-700 hover:bg-gray-50", active != "week") }
+		>
+			Week
+		</a>
+	</div>
+}
+
 templ calendarLegendRow(c CalendarSummary) {
 	<div class="px-4 py-3 flex items-center gap-3 text-sm flex-wrap">
 		<span class="w-3 h-3 rounded-full shrink-0 ring-1 ring-inset ring-black/10" style={ "background-color: " + colorOrDefault(c.Color) }></span>
@@ -170,6 +216,83 @@ templ monthDayCell(day MonthDay) {
 	</div>
 }
 
+// WeekView renders a single 7-day week across every calendar (own +
+// shared) visible to the viewer, one column per day.
+templ WeekView(username string, data WeekViewData) {
+	@Layout("Calendar", username) {
+		<div class="flex items-center justify-between mb-6 gap-4 flex-wrap">
+			<h1 class="text-2xl font-semibold">Calendar</h1>
+			<div class="flex gap-2 items-center flex-wrap">
+				<a href={ templ.URL(data.PrevWeekURL) } class="bg-white border border-gray-300 rounded-md px-3 py-1.5 text-sm font-medium text-gray-700 hover:bg-gray-50">&larr;</a>
+				<a href={ templ.URL(data.TodayURL) } class="bg-white border border-gray-300 rounded-md px-3 py-1.5 text-sm font-medium text-gray-700 hover:bg-gray-50">Today</a>
+				<a href={ templ.URL(data.NextWeekURL) } class="bg-white border border-gray-300 rounded-md px-3 py-1.5 text-sm font-medium text-gray-700 hover:bg-gray-50">&rarr;</a>
+				<span class="text-lg font-medium ml-2">{ data.RangeLabel }</span>
+				@viewSwitcher("week", data.MonthURL, "/web/calendar/week")
+				if data.HasWritable {
+					<a href="/web/calendar/new"
+						class="bg-indigo-600 text-white rounded-md px-3 py-1.5 text-sm font-medium hover:bg-indigo-700 ml-2">
+						New event
+					</a>
+				}
+			</div>
+		</div>
+
+		if len(data.Calendars) == 0 {
+			<p class="text-sm text-gray-500 mb-6">
+				You don't have any calendars yet — create one from the
+				<a href="/web/" class="text-indigo-600 hover:underline">dashboard</a> first.
+			</p>
+		} else {
+			<div class="grid grid-cols-7 gap-px bg-gray-200 border border-gray-200 rounded-lg overflow-hidden text-sm mb-6">
+				for _, d := range data.Days {
+					@weekDayHeaderCell(d)
+				}
+				for _, d := range data.Days {
+					@weekDayCell(d)
+				}
+			</div>
+
+			<div class="bg-white rounded-lg border border-gray-200 divide-y divide-gray-200">
+				for _, c := range data.Calendars {
+					@calendarLegendRow(c)
+				}
+			</div>
+		}
+	}
+}
+
+templ weekDayHeaderCell(day WeekDay) {
+	<div class={ "bg-gray-50 px-2 py-1.5 text-xs text-center", templ.KV("text-indigo-600 font-semibold", day.IsToday), templ.KV("text-gray-500 font-medium", !day.IsToday) }>
+		{ day.Weekday } <span class="text-gray-400">{ day.Month }</span> { fmt.Sprint(day.Day) }
+	</div>
+}
+
+templ weekDayCell(day WeekDay) {
+	<div class="bg-white min-h-[24rem] p-1.5 flex flex-col gap-1 align-top">
+		<a
+			href={ templ.URL("/web/calendar/new?date=" + day.Date) }
+			class="self-start text-xs text-gray-400 hover:text-indigo-600 mb-1"
+			title="New event"
+		>
+			+ new
+		</a>
+		for _, ev := range day.Events {
+			<a
+				href={ templ.URL(eventLinkURL(ev)) }
+				class="block truncate rounded px-1.5 py-0.5 text-xs hover:opacity-80"
+				style={ "background-color: " + colorOrDefault(ev.Color) + "22; color: " + eventTextColor(ev.Color) }
+				title={ ev.Summary }
+			>
+				<span class="inline-block w-1.5 h-1.5 rounded-full mr-1 ring-1 ring-inset ring-black/10" style={ "background-color: " + eventTextColor(ev.Color) }></span>
+				if !ev.AllDay && ev.TimeText != "" {
+					<span class="font-medium">{ ev.TimeText }</span>
+				}
+				{ " " + ev.Summary }
+			</a>
+		}
+	</div>
+}
+
 func eventLinkURL(ev EventSummary) string {
 	if ev.LinkURL != "" {
 		return ev.LinkURL