Add a Locus Pro-style toolbar readout: DMS coords + sunrise/sunset

The topbar's coordinate display was plain decimal degrees ("48.14611,
17.17722") — switched to DMS (48°08'46"N 17°10'38"E), the more
GPS-unit-like format Locus Pro itself uses, and made it click-to-copy
(plain decimal, since that's what pastes cleanly into another map/GPS
app — not the DMS text actually shown).

Added sunrise/sunset + a countdown to whichever's next, for the same
map-center point the coordinates already describe. Vendored SunCalc
(BSD-2-Clause, github.com/mourner/suncalc) rather than hand-rolling
the astronomical math — small, dependency-free, and correctness here
has real pitfalls (equation of time, refraction, polar day/night) a
first-pass reimplementation would risk getting subtly wrong.

Also added a test asserting every public/js/*.js module has a
versioned importmap entry in layout.erb — caught that overlays.js
(from the previous commit) was missing one, which would have quietly
skipped ASSET_VERSION's cache-busting for that file after every
deploy.

public/js/sun.js

@@ -0,0 +1,66 @@
+import { getTimes } from "/vendor/suncalc/suncalc.js";
+
+// A Locus Pro-style toolbar readout: DMS coordinates (plain decimal degrees
+// read less like a "GPS unit" and are harder to scan at a glance) plus
+// sunrise/sunset and a countdown to whichever comes next — both computed
+// for the map's current center, the same point the coordinates already
+// describe, not a GNSS fix (this app's coordinate readout was never tied
+// to having one).
+
+function toDMS(value, positiveLabel, negativeLabel) {
+  const label = value >= 0 ? positiveLabel : negativeLabel;
+  const abs = Math.abs(value);
+  const degrees = Math.floor(abs);
+  const minutesFull = (abs - degrees) * 60;
+  let minutes = Math.floor(minutesFull);
+  let seconds = Math.round((minutesFull - minutes) * 60);
+  // A seconds value that rounds up to 60 has to carry into minutes (and
+  // from there, in the rare case, into degrees) rather than print "60".
+  if (seconds === 60) {
+    seconds = 0;
+    minutes += 1;
+  }
+  const carriedDegrees = minutes === 60 ? degrees + 1 : degrees;
+  const carriedMinutes = minutes === 60 ? 0 : minutes;
+  return `${carriedDegrees}°${String(carriedMinutes).padStart(2, "0")}'${String(seconds).padStart(2, "0")}"${label}`;
+}
+
+export function formatCoords(lat, lng) {
+  return `${toDMS(lat, "N", "S")} ${toDMS(lng, "E", "W")}`;
+}
+
+function formatTime(date) {
+  return `${String(date.getHours()).padStart(2, "0")}:${String(date.getMinutes()).padStart(2, "0")}`;
+}
+
+function formatCountdown(ms) {
+  const totalMinutes = Math.max(0, Math.round(ms / 60000));
+  const hours = Math.floor(totalMinutes / 60);
+  const minutes = totalMinutes % 60;
+  return hours > 0 ? `${hours}h ${minutes}m` : `${minutes}m`;
+}
+
+const DAY_MS = 24 * 60 * 60 * 1000;
+
+// null when there's no sunrise/sunset to show at all — getTimes returns
+// null (not Invalid Date) for both on a polar day/night, per its own
+// comment in suncalc.js — the caller just hides the readout in that case
+// rather than showing something misleading.
+export function formatSunInfo(lat, lng, now = new Date()) {
+  const today = getTimes(now, lat, lng);
+  if (today.sunrise === null || today.sunset === null) return null;
+
+  let next;
+  if (now < today.sunrise) {
+    next = { label: "sunrise", at: today.sunrise };
+  } else if (now < today.sunset) {
+    next = { label: "sunset", at: today.sunset };
+  } else {
+    // Already past today's sunset — the next event is tomorrow's sunrise.
+    const tomorrow = getTimes(new Date(now.getTime() + DAY_MS), lat, lng);
+    next = tomorrow.sunrise === null ? null : { label: "sunrise", at: tomorrow.sunrise };
+  }
+
+  const countdown = next ? ` · ${formatCountdown(next.at - now)} to ${next.label}` : "";
+  return `${formatTime(today.sunrise)}–${formatTime(today.sunset)}${countdown}`;
+}