Refactor timestamp generation to use helper function

Introduces `PendingStore.nowRfc3339()` to consistently generate RFC3339
timestamps with second granularity. This avoids potential issues with
sub-second precision in filenames and aligns with common timestamp
formatting practices. The helper function is used in `CaseDetailScreen`
and `RecordingViewModel` to replace direct calls to
`Instant.now().toString()`. A new unit test verifies the expected
behavior of the helper function.

CLAUDE.md

@@ -19,6 +19,10 @@
 
 * CRITICAL: "cargo clippy" hat immer Recht!
 
+## Java
+
+* Java Home ist in /opt/android-studio/jbr
+
 ## HTML
 
 * Innerhalb von HTML-Seiten sind JS-Einbettungen ausdrücklich erlaubt und gewünscht, wenn sie für den modernen Look-And-Feel der Webseite erforderlich sind.

watch/wearos/app/src/main/java/com/doctate/watch/audio/PendingStore.kt

@@ -4,6 +4,8 @@ import android.util.Log
 import java.io.File
 import java.nio.file.Files
 import java.nio.file.StandardCopyOption
+import java.time.Instant
+import java.time.temporal.ChronoUnit
 import org.json.JSONObject
 
 /**
@@ -99,5 +101,15 @@ class PendingStore(private val dir: File) {
          *  `doctate-common::timestamp::recorded_at_to_filename_stem`. */
         fun recordedAtToFilenameStem(recordedAt: String): String =
             recordedAt.replace(':', '-')
+
+        /** Current UTC time as RFC3339 with second granularity, e.g.
+         *  `2026-04-15T10:32:00Z`. 1:1 to
+         *  `doctate-common::timestamp::now_rfc3339`. The truncation is
+         *  load-bearing: the server's filename parser expects exactly
+         *  `YYYY-MM-DDTHH-MM-SSZ` after the `:` → `-` substitution, and
+         *  `Instant.now().toString()` would otherwise leak microseconds
+         *  from the platform clock. */
+        fun nowRfc3339(): String =
+            Instant.now().truncatedTo(ChronoUnit.SECONDS).toString()
     }
 }

watch/wearos/app/src/main/java/com/doctate/watch/presentation/CaseDetailScreen.kt

@@ -34,6 +34,7 @@ import androidx.wear.compose.material3.ScreenScaffold
 import androidx.wear.compose.material3.Text
 import androidx.wear.input.RemoteInputIntentHelper
 import com.doctate.watch.DoctateApp
+import com.doctate.watch.audio.PendingStore
 import com.doctate.watch.domain.OnelinerState
 import com.doctate.watch.domain.displayText
 import com.doctate.watch.domain.isManual
@@ -79,7 +80,7 @@ fun CaseDetailScreen(
                 // Optimistic local update — UI flips to Manual immediately.
                 app.caseStore.setOnelinerLocal(
                     caseId,
-                    OnelinerState.Manual(text, setAt = Instant.now().toString()),
+                    OnelinerState.Manual(text, setAt = PendingStore.nowRfc3339()),
                 )
                 // Push the edit to the server. Fire-and-forget: the local
                 // state stays even if the network is down. Edits before

watch/wearos/app/src/main/java/com/doctate/watch/presentation/RecordingViewModel.kt

@@ -14,7 +14,6 @@ import com.doctate.watch.audio.PendingUpload
 import com.doctate.watch.domain.CaseStore
 import com.doctate.watch.sync.SyncKick
 import com.doctate.watch.sync.SyncTrigger
-import java.time.Instant
 import java.util.concurrent.atomic.AtomicBoolean
 import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
@@ -98,7 +97,7 @@ class RecordingViewModel(
     private fun startRecordingFlow() {
         finalizationStarted.set(false)
         recordingJob = viewModelScope.launch {
-            val recordedAt = Instant.now().toString()
+            val recordedAt = PendingStore.nowRfc3339()
             val target = pendingStore.audioPathFor(caseId, recordedAt)
             try {
                 withContext(Dispatchers.IO) { recorder.start(target) }
@@ -140,7 +139,7 @@ class RecordingViewModel(
             dispatch(RecordingEvent.UploadFailed("Stop failed: ${e.message}", transient = false))
             return
         }
-        val recordedAt = pendingRecordedAt ?: Instant.now().toString()
+        val recordedAt = pendingRecordedAt ?: PendingStore.nowRfc3339()
         pendingRecordedAt = null
         try {
             withContext(Dispatchers.IO) {

watch/wearos/app/src/test/java/com/doctate/watch/audio/PendingStoreTest.kt

@@ -100,4 +100,17 @@ class PendingStoreTest {
         assertThat(found.recordedAt).isEqualTo("2026-04-26T10:00:00Z")
         assertThat(found.file.absolutePath).isEqualTo(audio.absolutePath)
     }
+
+    /** Regression guard: subsecond precision must be stripped. A single
+     *  microsecond leak would feed the server filename parser
+     *  `YYYY-MM-DDTHH-MM-SS.NNNNNNZ.m4a`, which it treats as malformed —
+     *  the resulting `<time datetime>` is empty and the day-grouping
+     *  falls back to `today`, producing duplicate "Heute" headers.
+     *  Mirrors `now_rfc3339_has_no_subsecond_component` in the Rust
+     *  `doctate-common::timestamp` crate. */
+    @Test fun nowRfc3339_has_no_subsecond_component() {
+        val now = PendingStore.nowRfc3339()
+        assertThat(now).doesNotContain(".")
+        assertThat(now).endsWith("Z")
+    }
 }