Merge branch 'feat/23-world-clock-seconds' into release/v1.0.0

# Conflicts:
#	app/src/main/java/de/jeanlucmakiola/clockula/backup/BackupEngine.kt
#	app/src/main/java/de/jeanlucmakiola/clockula/data/backup/BackupCodec.kt
#	app/src/main/java/de/jeanlucmakiola/clockula/data/backup/BackupDto.kt
#	app/src/main/java/de/jeanlucmakiola/clockula/data/prefs/SettingsPrefs.kt
#	app/src/main/java/de/jeanlucmakiola/clockula/domain/backup/BackupContent.kt
#	app/src/test/java/de/jeanlucmakiola/clockula/data/backup/BackupCodecTest.kt
#	app/src/test/java/de/jeanlucmakiola/clockula/ui/settings/SettingsViewModelTest.kt
#	docs/ARCHITECTURE.md
#	docs/BACKUP.md

docs/BACKUP.md

@@ -159,6 +159,7 @@ device or after a reboot (`docs/PLAN.md` §5). Every imported timer lands
   "default_alarm_silence_after_minutes": 10,
   "default_timer_silence_after_minutes": 10,
   "volume_buttons_while_ringing": "CONTROL_VOLUME",
+  "world_clock_show_seconds": false,
   "timer_presets": [60000, 120000, 180000, 300000, 600000, 900000, 1800000, 3600000],
   "bedtime": {
     "enabled": false,
@@ -199,6 +200,10 @@ hour). A file without them, from before the setting existed, imports as `10`,
 the value it was made with. A value of 60 or more reads as 0, "Never" (which
 rings for that long anyway); a negative one reads as the default, 10.
 
+Files from before `world_clock_show_seconds` existed import with it off, its
+default. It travels with the settings but is not a clock default: nothing an
+alarm or timer inherits depends on it.
+
 Every numeric/duration value is clamped on *apply* using the same ranges and encoding
 as the existing preference setters, never on parse.