fix(lotw): 呼号冲突批量全阻时也进预览，呼号不符改为显示记录≠证书

整批记录都被呼号冲突挡住（0 条可传）时，统计闸门直接弹「N QSO(s) can't be uploaded」
消息并返回，带【改写为…】【换一张证书】两个动作的预览弹窗根本走不到，那批记录无从
处理。现在只要原因里有呼号冲突就放行到预览：0 条可传也出预览（显示 0 QSO(s) + 冲突
提示 + 两个动作），上传键置灰——以前点确认会返回“预览已过期”。其它原因的 0 条可传
批次保持原消息弹窗不变。

「MY callsign does not match the certificate」的示例值由某条记录的对方呼号改为
「记录呼号 ≠ 证书呼号」，把需要协调的两个值都打出来（旧文案读起来像证书呼号）。

空预览不再显示空的日期区间。

新增 LoTWUploadMessagesTest 3 例：冲突批量必须进预览、无冲突的 0 条可传批次保持消息、
有待传记录时不走冲突兜底；仓库层用例新增：全阻批量仍返回带冲突清单的预览、且无载荷
时确认安全地按“过期”失败。

core/data/src/main/java/com/rtbishop/look4sat/core/data/lotw/LoTWSigner.kt

@@ -37,7 +37,12 @@ internal class LoTWSigner(private val config: LoTWConfig) {
         val call = record.theirCallsign.trim().uppercase(Locale.US)
         if (record.status != QsoStatus.COMPLETE || !call.matches(Regex("[A-Z0-9]+(/[A-Z0-9]+)*")) ||
             !call.any(Char::isLetter) || !call.any(Char::isDigit)) fail(LoTWProblem.INVALID_CONTACT, call)
-        if (!record.myCallsign.trim().equals(key.info.callsign, true)) fail(LoTWProblem.CALLSIGN_MISMATCH, call)
+        // Report the two callsigns the operator has to reconcile (record vs certificate). A generic
+        // sample — the opposite station's call — says nothing about which side is wrong, which is
+        // exactly what a "MY callsign does not match the certificate" message must tell.
+        if (!record.myCallsign.trim().equals(key.info.callsign, true)) {
+            fail(LoTWProblem.CALLSIGN_MISMATCH, "${record.myCallsign.trim()} ≠ ${key.info.callsign}")
+        }
         val date = utc(record.startUtcMillis, "yyyy-MM-dd")
         // A record dated after "now" gets its own message: it happens when the operator
         // logged against a pass that had not started yet (out-of-window flow), and "fix the

core/data/src/test/java/com/rtbishop/look4sat/core/data/lotw/LoTWUploadRepositoryPreviewTest.kt

@@ -22,6 +22,7 @@ import com.rtbishop.look4sat.core.domain.logbook.QsoStatus
 import com.rtbishop.look4sat.core.domain.repository.LoTWOperationException
 import com.rtbishop.look4sat.core.domain.repository.LoTWProblem
 import com.rtbishop.look4sat.core.domain.repository.LoTWStation
+import com.rtbishop.look4sat.core.domain.repository.LoTWUploadResult
 import java.io.File
 import kotlinx.coroutines.runBlocking
 import org.junit.Assert.assertEquals
@@ -120,6 +121,55 @@ class LoTWUploadRepositoryPreviewTest {
         }
     }
 
+    /** Nothing signable at all: the preview still comes back (count 0) with the conflicts listed,
+     *  so the UI can offer the rewrite / use-another-certificate actions instead of a dead end. */
+    @Test
+    fun `fully blocked batch still returns a preview with the conflicts`() {
+        runBlocking {
+            val storage = MemStorage()
+            val repo = LoTWUploadRepository(
+                storage,
+                { LoTWConfig(File("src/main/assets/lotw/config.tq6").inputStream()) },
+                now = { System.currentTimeMillis() }
+            )
+            repo.importCertificate(fixture("test_tqsl_empty.p12"), charArrayOf())
+            repo.saveStation(LoTWStation(grid = "OL62TI"))
+            val start = 1_787_000_000_000L
+            val preview = repo.prepare(
+                listOf(
+                    sampleRecord(start, "BH6RJD", "XX0YY"),
+                    sampleRecord(start + 60_000L, "BG7QBL", "XX0ZZ")
+                ),
+                resubmit = false
+            )
+            assertEquals(0, preview.count)
+            assertEquals(2, preview.unavailableSkipped)
+            assertEquals(listOf(start, start + 60_000L), preview.callsignConflicts)
+            assertEquals(2, preview.unavailableReasons[LoTWProblem.CALLSIGN_MISMATCH])
+            assertEquals(0, preview.missingCallsign)
+            // No payload was prepared: confirming this preview must fail as expired, not crash.
+            assertTrue(repo.upload(preview.id) is LoTWUploadResult.ExpiredPreview)
+        }
+    }
+
+    /** The mismatch reason names both callsigns (record vs certificate). The old detail showed the
+     *  opposite station's call, which told the operator nothing about which side to fix. */
+    @Test
+    fun `callsign mismatch detail names the record and the certificate callsign`() {
+        runBlocking {
+            val storage = MemStorage()
+            val repo = LoTWUploadRepository(
+                storage,
+                { LoTWConfig(File("src/main/assets/lotw/config.tq6").inputStream()) },
+                now = { System.currentTimeMillis() }
+            )
+            repo.importCertificate(fixture("test_tqsl_empty.p12"), charArrayOf())
+            repo.saveStation(LoTWStation(grid = "OL62TI"))
+            val audit = repo.audit(listOf(sampleRecord(1_787_000_000_000L, "BH6RJD", "XX0YY")))
+            assertEquals("XX0YY ≠ BA7OPF", audit.details[LoTWProblem.CALLSIGN_MISMATCH])
+        }
+    }
+
     private fun sampleRecord(start: Long, call: String, myCallsign: String) = QsoRecord(
         id = start,
         startUtcMillis = start,