feat(contacts): drop {age} from default titles, disclaim it when added

A FREQ=YEARLY event has one static title, so {age} is only a sync-time snapshot
and can look wrong on far-future occurrences. Keep it out of the default
templates ({name}'s birthday / anniversary), and when a user does add {age} in
the title-format editor, show a short disclaimer about the snapshot behaviour.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/src/main/java/de/jeanlucmakiola/calendula/ui/settings/SettingsScreen.kt

@@ -1251,6 +1251,16 @@ private fun SpecialDatesTemplateDialog(
                     style = MaterialTheme.typography.bodySmall,
                     color = MaterialTheme.colorScheme.onSurfaceVariant,
                 )
+                // Only warn about {age}'s snapshot behaviour once the user has
+                // actually put it in the template.
+                if (text.contains("{age}")) {
+                    Spacer(Modifier.height(8.dp))
+                    Text(
+                        text = stringResource(R.string.settings_special_dates_template_age_note),
+                        style = MaterialTheme.typography.bodySmall,
+                        color = MaterialTheme.colorScheme.tertiary,
+                    )
+                }
             }
         },
         confirmButton = {