release: cut v1.2.1 — event-form polish

Version bumped to 1.2.1 / 10. No code changes beyond the version — 1.2.1 is
the reviewed-and-approved form polish: card design system, optional fields
with settings defaults, reworked reminders, OptionCard dialogs app-wide,
expressive theme on standard springs, direction-aware today jump, IME fix.
CHANGELOG [1.2.1] carries the details.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

app/build.gradle.kts

@@ -23,8 +23,8 @@ android {
         applicationId = "de.jeanlucmakiola.calendula"
         minSdk = 29
         targetSdk = 36
-        versionCode = 9
-        versionName = "1.2.0"
+        versionCode = 10
+        versionName = "1.2.1"
 
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }