Polish the mobile nav dropdown; rename Day to Day Detail (#121)

- Compact the mobile menu: narrower panel (208px), tighter rows, and the nav
  list now stretches to the panel width and left-aligns (it was centering because
  the base .view-nav align-self:center overrode the panel's stretch).
- Stylish separation between entries: an inset hairline between each nav item,
  suppressed around the active pill so nothing crosses it.
- Rename the "Day" view to "Day Detail" across the app nav, and add it to the
  climate/city page nav (base.html.j2), which was missing it.

templates/base.html.j2

@@ -37,6 +37,7 @@
         <nav class="view-nav" aria-label="Views">
         <a href="{{ base }}/">Weekly</a>
         <a href="{{ base }}/calendar">Calendar</a>
+        <a href="{{ base }}/day">Day Detail</a>
         <a href="{{ base }}/compare">Compare</a>
         <a href="{{ base }}/climate"{% if section == 'climate' %} class="active"{% endif %}>Climate</a>
       </nav>