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.

views/index.erb

@@ -1,7 +1,10 @@
 <div id="app">
   <header class="topbar">
     <span class="topbar__brand" title="rev <%= revision %>">MapTool</span>
-    <span class="topbar__coords"></span>
+    <span class="topbar__center">
+      <span class="topbar__coords"></span>
+      <span class="topbar__sun" hidden></span>
+    </span>
     <span class="topbar__offline-status" hidden></span>
     <div class="topbar__auth">
       <% if logged_in %>