Make the day-bar sleep pill a one-tap toggle

Once the big timer scrolls away, the pill in the day bar is the only thing
still showing the sleep state — but acting on it meant scrolling back up to
the quick actions. Tapping the pill now logs the boundary that ends the state
it displays: sleep-end while asleep, sleep-start while awake. It routes
through quickLog(), so the snackbar and its undo behave exactly as they do
from the buttons, and the state is read from currentSleepState() rather than
the cached bigClockState so a tap can't act on a stale render.

The pill becomes a real <button>, which brings keyboard operation along for
free. In standby it is visibility:hidden, so while the big card is on screen
it is neither clickable nor tab-reachable, and the toggle is live exactly when
the pill is visible.

The .day-bar button padding and :disabled rules are scoped to :not(.bar-clock)
so they don't start outranking the pill's own sizing, and the default accent
button background is reset since the asleep/awake classes paint it.

src/index.html

@@ -81,11 +81,13 @@
       <section class="day-bar">
         <!-- Compact twin of the big timer below: invisible (but keeping its
              slot) while the big card is on screen, shown once it scrolls
-             away. Hidden entirely until a sleep event exists. -->
-        <div id="bar-clock" class="bar-clock" hidden>
+             away. Hidden entirely until a sleep event exists. Tapping it logs
+             the boundary that flips the current state (asleep → sleep end,
+             awake → sleep start). -->
+        <button type="button" id="bar-clock" class="bar-clock" hidden>
           <span id="bar-clock-icon" aria-hidden="true"></span>
           <span id="bar-clock-time"></span>
-        </div>
+        </button>
         <button type="button" id="day-prev" class="ghost" aria-label="Previous day">←</button>
         <!-- A browser won't let us shorten the text a native date input shows,
              so the face button carries a compact year-less date and the real