fix(notification): give reminders Calendula's own status-bar mark (#83)

The status bar draws a notification's small icon from its alpha channel
alone, so the silhouette is all that distinguishes an app there — and ours
was the stock Material "event" glyph, the same shape the system's date
surfaces and every other calendar app use.

Redrawn at 24dp from the launcher mark rather than scaled down from it: the
numeral is dropped and the bloom's petals are filled instead of stroked,
both of which turn to mush at this size. The bloom is sized and placed for
legibility over fidelity, and the calendar body's opening is derived from
where the bloom would collide with it.

The shade needs no change — since Android 12 its header shows the launcher
icon, which is already unmistakable.

design/icon/calendula_notification.svg

@@ -0,0 +1,12 @@
+<svg width="24" height="24" viewBox="0 0 24 24" fill="none" xmlns="http://www.w3.org/2000/svg">
+<path d="M1.4 5.4H18.6M18.6 9.43V4.7C18.6 2.99 17.21 1.6 15.5 1.6H4.5C2.79 1.6 1.4 2.99 1.4 4.7V15.7C1.4 17.41 2.79 18.8 4.5 18.8H9.63" stroke="black" stroke-width="1.9" stroke-linecap="round" stroke-linejoin="round"/>
+<path d="M17.6 16.35Q20.42 18.65 23.25 16.35Q20.42 14.05 17.6 16.35Z" fill="black"/>
+<path d="M17.26 17.16Q17.63 20.79 21.26 21.16Q20.89 17.53 17.26 17.16Z" fill="black"/>
+<path d="M16.45 17.5Q14.15 20.33 16.45 23.15Q18.75 20.33 16.45 17.5Z" fill="black"/>
+<path d="M15.64 17.16Q12.01 17.53 11.64 21.16Q15.27 20.79 15.64 17.16Z" fill="black"/>
+<path d="M15.3 16.35Q12.47 14.05 9.65 16.35Q12.47 18.65 15.3 16.35Z" fill="black"/>
+<path d="M15.64 15.54Q15.27 11.91 11.64 11.54Q12.01 15.17 15.64 15.54Z" fill="black"/>
+<path d="M16.45 15.2Q18.75 12.38 16.45 9.55Q14.15 12.38 16.45 15.2Z" fill="black"/>
+<path d="M17.26 15.54Q20.89 15.17 21.26 11.54Q17.63 11.91 17.26 15.54Z" fill="black"/>
+<circle cx="16.45" cy="16.35" r="2.5" fill="black"/>
+</svg>