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/css/style.css

@@ -27,13 +27,32 @@ html, body {
   color: #fff;
 }
 
-.topbar__coords {
+.topbar__center {
   margin: 0 auto;
+  display: flex;
+  align-items: center;
+  gap: 14px;
+}
+
+.topbar__coords,
+.topbar__sun {
   font-size: 12px;
   font-variant-numeric: tabular-nums;
   color: #bbb;
 }
 
+.topbar__coords {
+  cursor: pointer;
+}
+
+.topbar__coords:hover {
+  color: #fff;
+}
+
+.topbar__sun[hidden] {
+  display: none;
+}
+
 .topbar__offline-status {
   width: 8px;
   height: 8px;