fix(lotw): 空呼号记录按证书上传并回填，呼号冲突可选改写或换证书

证书装好之前记录的 QSO 自己呼号存空，签名时被判 CALLSIGN_MISMATCH，整批上传失败。
现在这类记录改用当前证书呼号签名，不再拒签：预览提示「其中 N 条记录没有呼号，将按证书
XXX 上传」，上传成功后仅把这些记录的空呼号回填为证书呼号（只填空值，经 save() 写入以
保持去重键一致，不动时间/频率/模式/对方呼号/上传状态与确认状态）。

自己呼号非空且与证书不同的记录仍拒签（不冒签他人记录），但预览给出两个选择：
「改写为 XXX」把冲突记录的自己呼号改成当前证书呼号后即可重传；「换一张证书」在设置页
关掉日志本并打开 LoTW 配置导入另一张证书（雷达页提示去设置页导入）。

新增单测：空呼号签名与计数、冲突记录 id、markUploaded 只填空值、rewriteMyCallsign 只改
冲突记录；并修正测试夹具 MemStorage.read 返回共享数组（被调用方 fill(0) 后破坏已存证书，
与文件存储行为不一致）导致的问题。

feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/LogPage.kt

@@ -262,7 +262,9 @@ fun LogPage(
                 preview = preview,
                 busy = logUiState.busy,
                 onConfirm = logViewModel::confirmUpload,
-                onDismiss = logViewModel::dismissPreview
+                onDismiss = logViewModel::dismissPreview,
+                onRewriteCallsign = logViewModel::rewriteCallsignConflicts,
+                onSwitchCertificate = logViewModel::switchCertificateForConflicts
             )
         }
     }
@@ -417,7 +419,9 @@ private fun UploadPreviewDialog(
     preview: com.rtbishop.look4sat.core.domain.repository.LoTWUploadPreview,
     busy: Boolean,
     onConfirm: () -> Unit,
-    onDismiss: () -> Unit
+    onDismiss: () -> Unit,
+    onRewriteCallsign: () -> Unit,
+    onSwitchCertificate: () -> Unit
 ) {
     AlertDialog(
         onDismissRequest = onDismiss,
@@ -464,6 +468,32 @@ private fun UploadPreviewDialog(
                     }
                     Text(parts.joinToString(" · "), fontSize = 12.sp, color = MaterialTheme.colorScheme.error)
                 }
+                if (preview.missingCallsign > 0) {
+                    // Logged while no certificate was installed; signed with the certificate's
+                    // callsign instead of being refused.
+                    Text(
+                        stringResource(R.string.prefs_logbook_callsign_missing, preview.missingCallsign, preview.callsign),
+                        fontSize = 12.sp,
+                        color = MaterialTheme.colorScheme.primary
+                    )
+                }
+                if (preview.callsignConflicts.isNotEmpty()) {
+                    // These name another callsign than the certificate: rewrite them with this
+                    // certificate's callsign, or upload them under the other certificate.
+                    Text(
+                        stringResource(R.string.prefs_logbook_callsign_different, preview.callsignConflicts.size, preview.callsign),
+                        fontSize = 12.sp,
+                        color = MaterialTheme.colorScheme.error
+                    )
+                    Row(horizontalArrangement = Arrangement.spacedBy(8.dp)) {
+                        TextButton(onClick = onRewriteCallsign, enabled = !busy) {
+                            Text(stringResource(R.string.prefs_logbook_callsign_rewrite, preview.callsign), fontSize = 12.sp)
+                        }
+                        TextButton(onClick = onSwitchCertificate, enabled = !busy) {
+                            Text(stringResource(R.string.prefs_logbook_callsign_switch), fontSize = 12.sp)
+                        }
+                    }
+                }
                 Text(preview.contacts.joinToString("\n") { it }, fontSize = 12.sp, maxLines = 8)
             }
         },

feature/radar/src/main/java/com/rtbishop/look4sat/feature/radar/LogViewModel.kt

@@ -343,7 +343,7 @@ class LogViewModel(
             if (result is LoTWUploadResult.Accepted && lastUploadedIds.isNotEmpty()) {
                 // Mark the submitted QSOs as uploaded (distinct from confirmed) and stamp
                 // the station grids this batch went out under.
-                qsoRepository.markUploaded(lastUploadedIds, preview.grids)
+                qsoRepository.markUploaded(lastUploadedIds, preview.grids, preview.callsign)
                 lastUploadedIds = emptyList()
             }
             val msg = when (result) {
@@ -368,6 +368,34 @@ class LogViewModel(
 
     fun dismissPreview() = _uiState.update { it.copy(preview = null) }
 
+    /**
+     * Operator chose "rewrite" on the callsign conflict: the refused records get this certificate's
+     * callsign so the next upload can sign them. The prepared batch is dropped — nothing was sent.
+     */
+    fun rewriteCallsignConflicts() {
+        val preview = _uiState.value.preview ?: return
+        val ids = preview.callsignConflicts
+        if (ids.isEmpty()) return
+        viewModelScope.launch {
+            _uiState.update { it.copy(busy = true) }
+            val changed = qsoRepository.rewriteMyCallsign(ids, preview.callsign)
+            lotwUploadRepository.discardPreview()
+            lastUploadedIds = emptyList()
+            _uiState.update {
+                it.copy(busy = false, preview = null, message = "$changed record(s) rewritten to ${preview.callsign} — upload again")
+            }
+        }
+    }
+
+    /** Operator chose "use another certificate": that certificate is imported on the settings page. */
+    fun switchCertificateForConflicts() {
+        lotwUploadRepository.discardPreview()
+        lastUploadedIds = emptyList()
+        _uiState.update {
+            it.copy(preview = null, message = "Import the other callsign's certificate in Settings → LoTW upload, then upload again")
+        }
+    }
+
     fun dismissWavelogPreview() = _uiState.update { it.copy(wavelogPreview = null) }
 
     /**