Add hourly day timeline and red now indicators to the calendar

Days with 4+ entries open with an hour-grid timeline in the day editor:
untimed entries in an all-day strip, timed ones positioned by start/end
with side-by-side columns for overlaps, click-to-edit. Layout math lives
in a pure, unit-tested module (timelineLayout.js).

Today's month-grid cell gets a vertical red slider positioned by the
fraction of the day elapsed; the timeline gets the classic horizontal
red current-time line. Both tick every minute with cleanup on unmount,
and the initial positioning runs unconditionally while the node is
still detached (the isConnected self-heal gates only interval ticks).

Also splits entryRow rendering out of dayEditor.js to stay under the
500-line cap.

public/js/views/calendar.js

@@ -22,7 +22,27 @@ import { makeChipDraggable, makeDayDropTarget } from './dragdrop.js';
 
 const WEEKDAYS = ['Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat', 'Sun'];
 
+// The red "now" slider's 60s interval lives in module state (only one
+// calendar is ever mounted) — same lifecycle convention as flipclock.js's
+// countdown: stopNowTicker() runs at the top of every renderCalendar so a
+// re-render (refreshTrip) never leaks or double-ticks, and a hashchange
+// handler stops it on navigation away from the trip page.
+let activeTimer = null;
+let activeHashHandler = null;
+
+function stopNowTicker() {
+  if (activeTimer) {
+    clearInterval(activeTimer);
+    activeTimer = null;
+  }
+  if (activeHashHandler) {
+    window.removeEventListener('hashchange', activeHashHandler);
+    activeHashHandler = null;
+  }
+}
+
 export function renderCalendar(tctx) {
+  stopNowTicker();
   const { trip, entries } = tctx.trip;
   const currency = trip.currency || 'USD';
 
@@ -100,6 +120,8 @@ export function renderCalendar(tctx) {
   for (const label of WEEKDAYS) header.appendChild(el('div', { class: 'cal-weekday' }, label));
   cal.appendChild(header);
 
+  const todayKey = ymd(new Date());
+  let todayCell = null;
   for (const week of weeks) {
     // Each week is a stay-bands strip (all-day bars) above a row of day cells.
     const weekEl = el('div', { class: 'cal-week' });
@@ -107,11 +129,16 @@ export function renderCalendar(tctx) {
     if (bands) weekEl.appendChild(bands);
     const daysRow = el('div', { class: 'cal-week-days' });
     for (const date of week) {
-      daysRow.appendChild(dayCell(date, rangeStart, rangeEnd, byDate, contByDate, dropoffByDate, entriesById, tctx, currency));
+      const cell = dayCell(date, rangeStart, rangeEnd, byDate, contByDate, dropoffByDate, entriesById, tctx, currency);
+      if (ymd(date) === todayKey) todayCell = cell;
+      daysRow.appendChild(cell);
     }
     weekEl.appendChild(daysRow);
     cal.appendChild(weekEl);
   }
+  // Red "now" slider: only when today falls inside the rendered week rows
+  // (a past/future trip's grid may not include it at all).
+  if (todayCell) wireNowSlider(todayCell);
 
   // A cancelled drag (released outside a cell) fires dragend on the source chip,
   // which bubbles up here — sweep any lingering drop highlight.
@@ -150,6 +177,38 @@ function syncTransportsButton(tctx) {
   return btn;
 }
 
+// A vertical red line through today's cell, positioned by the fraction of the
+// day elapsed (00:00 left edge -> 24:00 right edge), with a dot on top — the
+// "slider" that moves through the cell over the day. Updates every 60s.
+function wireNowSlider(cell) {
+  cell.classList.add('cal-today');
+  const slider = el('div', { class: 'cal-now-slider' }, el('span', { class: 'cal-now-dot' }));
+  cell.appendChild(slider);
+
+  function position() {
+    const now = new Date();
+    const frac = (now.getHours() * 60 + now.getMinutes()) / 1440;
+    slider.style.left = `${frac * 100}%`;
+  }
+
+  // The isConnected self-heal only applies to interval ticks: the initial
+  // position() runs while the calendar section is still detached (tripDetail
+  // mounts it after renderCalendar returns), and gating it would leave the
+  // slider unpositioned until the first 60s tick.
+  function tick() {
+    if (!slider.isConnected) {
+      stopNowTicker();
+      return;
+    }
+    position();
+  }
+
+  position();
+  activeTimer = setInterval(tick, 60000);
+  activeHashHandler = stopNowTicker;
+  window.addEventListener('hashchange', activeHashHandler);
+}
+
 function dayCell(date, rangeStart, rangeEnd, byDate, contByDate, dropoffByDate, entriesById, tctx, currency) {
   const key = ymd(date);
   const inRange = date >= rangeStart && date <= rangeEnd;