feat(timezone): let the picker search by abbreviation

Search matched city, id, and the long localized name but not the
abbreviation, so typing "CEST" found nothing. Match it too: an exact
abbreviation hit ranks just under a city prefix, so typing an abbreviation
gathers every zone that shows it (all the CEST zones at once). It matches
the region-resolved abbreviation — i.e. exactly what the row displays.

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

app/src/test/java/de/jeanlucmakiola/calendula/domain/TimeZoneCatalogTest.kt

@@ -105,6 +105,19 @@ class TimeZoneCatalogTest {
         assertThat(filter("europe/berlin").map { it.id }).contains("Europe/Berlin")
     }
 
+    @Test
+    fun `query matches the abbreviation, case-insensitively`() {
+        // "cest" isn't a city, id, or substring of "Central European Summer
+        // Time", so the only way these match is via the abbreviation.
+        val hits = filter("cest")
+        assertThat(hits).isNotEmpty()
+        assertThat(hits.map { it.id }).contains("Europe/Berlin")
+        // Every hit genuinely carries that abbreviation — nothing bled in.
+        assertThat(hits.all { it.shortName.equals("CEST", ignoreCase = true) }).isTrue()
+        // Case doesn't matter.
+        assertThat(filter("CEST").map { it.id }).isEqualTo(hits.map { it.id })
+    }
+
     @Test
     fun `a city starting with the query outranks one merely containing it`() {
         val ids = filter("york").map { it.id }