fix: address Copilot review — keyboard trap, midnight formatting, nprofile hint

- MonthGrid: exactly one gridcell must stay tab-focusable. When no day is
  selected and the displayed month doesn't contain today (e.g. after a
  PageUp/PageDown jump), every cell previously got tabIndex=-1, trapping
  keyboard users out of the grid. Falls back to the 1st of the month.
- calendarEvents: formatEventTimeRange treated `end` as inclusive when
  checking same-day, so a time-based event ending exactly at local
  midnight formatted as a cross-day range even though eventDateKeys()
  attributes it to the start day only. Now compares against end-1ms,
  consistent with eventDateKeys().
- CalendarFilters: the author placeholder/error text only mentioned
  npub/hex even though nprofile is accepted (resolveAuthorInput handles
  it) — updated both to mention all three.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BYiUtZMQeA5RHggQw73wto

src/apps/calendar/CalendarFilters.tsx

@@ -80,13 +80,13 @@ export function CalendarFilters({ filters, onChange, authorError, resolvedAuthor
         </Label>
         <Input
           id="calendar-filter-author"
-          placeholder="npub or hex pubkey"
+          placeholder="npub, nprofile, or hex pubkey"
           value={filters.authorInput}
           onChange={(event) => set('authorInput', event.target.value)}
           aria-invalid={authorError || undefined}
           className="h-8 text-xs"
         />
-        {authorError && <p className="text-[11px] text-destructive">Not a valid npub or hex pubkey.</p>}
+        {authorError && <p className="text-[11px] text-destructive">Not a valid npub, nprofile, or hex pubkey.</p>}
       </div>
 
       <div className="space-y-1.5">

src/apps/calendar/MonthGrid.tsx

@@ -48,6 +48,13 @@ export function MonthGrid({
   const todayKey = localDateKey(today);
   const cellRefs = useRef(new Map<string, HTMLButtonElement>());
 
+  // Exactly one cell must be tab-focusable, or a keyboard user who tabs away
+  // and back can never re-enter the grid. Prefer the selected day, then
+  // today if it's in the displayed month, and only otherwise fall back to
+  // the 1st — e.g. after PageUp/PageDown lands on a month with neither.
+  const isTodayInMonth = today.getFullYear() === monthAnchor.getFullYear() && today.getMonth() === monthIndex;
+  const focusKey = selectedDate ?? (isTodayInMonth ? todayKey : localDateKey(new Date(monthAnchor.getFullYear(), monthIndex, 1)));
+
   const focusDate = (date: Date) => {
     const key = localDateKey(date);
     onSelectDate(key, { focus: true });
@@ -121,7 +128,7 @@ export function MonthGrid({
                   const isCurrentMonth = date.getMonth() === monthIndex;
                   const isToday = key === todayKey;
                   const isSelected = key === selectedDate;
-                  const isFocusable = selectedDate ? isSelected : isToday && isCurrentMonth;
+                  const isFocusable = key === focusKey;
 
                   return (
                     <button

src/lib/calendarEvents.test.ts

@@ -199,4 +199,25 @@ describe('formatEventTimeRange', () => {
     )!;
     expect(formatEventTimeRange(parsed)).toContain('–');
   });
+
+  it('treats a time-based event ending exactly at local midnight as ending on the start day, not the next', () => {
+    // `end` is exclusive, so this instant belongs to the start day, same as eventDateKeys() would attribute it.
+    const start = new Date(2026, 5, 1, 23, 0, 0);
+    const end = new Date(2026, 5, 2, 0, 0, 0);
+    const parsed = parseCalendarEvent(
+      makeEvent({
+        kind: TIME_BASED_KIND,
+        tags: [
+          ['d', 'a'],
+          ['title', 'T'],
+          ['start', String(Math.floor(start.getTime() / 1000))],
+          ['end', String(Math.floor(end.getTime() / 1000))],
+        ],
+      }),
+    )!;
+
+    const startDate = start.toLocaleDateString(undefined, { year: 'numeric', month: 'long', day: 'numeric' });
+    const expected = `${startDate}, ${start.toLocaleTimeString(undefined, { hour: 'numeric', minute: '2-digit' })} – ${end.toLocaleTimeString(undefined, { hour: 'numeric', minute: '2-digit' })}`;
+    expect(formatEventTimeRange(parsed)).toBe(expected);
+  });
 });

src/lib/calendarEvents.ts

@@ -225,14 +225,18 @@ export function formatEventTimeRange(parsed: ParsedCalendarEvent): string {
     return `${formatAllDayDate(parsed.start)} – ${formatAllDayDate(lastDay)}`;
   }
 
-  const sameDay = localDateKey(parsed.start) === localDateKey(parsed.end);
   const startDate = parsed.start.toLocaleDateString(undefined, { year: 'numeric', month: 'long', day: 'numeric' });
   if (parsed.start.getTime() === parsed.end.getTime()) {
     return `${startDate} at ${formatTime(parsed.start)}`;
   }
+  // `end` is exclusive, so an event ending exactly at midnight belongs to
+  // the *previous* instant's day — the same day `eventDateKeys()` puts it
+  // on — not the day `end` technically ticks over into.
+  const lastInstant = new Date(parsed.end.getTime() - 1);
+  const sameDay = localDateKey(parsed.start) === localDateKey(lastInstant);
   if (sameDay) {
     return `${startDate}, ${formatTime(parsed.start)} – ${formatTime(parsed.end)}`;
   }
-  const endDate = parsed.end.toLocaleDateString(undefined, { year: 'numeric', month: 'long', day: 'numeric' });
+  const endDate = lastInstant.toLocaleDateString(undefined, { year: 'numeric', month: 'long', day: 'numeric' });
   return `${startDate} ${formatTime(parsed.start)} – ${endDate} ${formatTime(parsed.end)}`;
 }