fix: passband RX update now uses full Doppler round-trip instead of pure passband mapping

When adjusting RX in passband mode (via +/- buttons or slider), the old
code used TransponderMapper.mapDownlinkToUplink (pure passband mapping
without Doppler compensation), producing ~10kHz error at LEO velocities.

Fix: use DopplerFrequencyCalculator.computeUplinkFromDownlinkWithOffset
for the full TX-from-RX round-trip, matching the RX→PASSBAND button
onClick logic. Also fixed frame mismatch: position now uses txLow/txRange
(Doppler-shifted frame) consistently.

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/model/Constants.kt

@@ -0,0 +1,23 @@
+/*
+ * Look4Sat. Amateur radio satellite tracker and pass predictor.
+ * Copyright (C) 2019-2026 Arty Bishop and contributors.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <https://www.gnu.org/licenses/>.
+ */
+package com.rtbishop.look4sat.core.domain.model
+
+object Constants {
+    const val FREQ_OFFSET_MIN_HZ = -50_000L
+    const val FREQ_OFFSET_MAX_HZ = 50_000L
+}

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/model/SatStatus.kt

@@ -23,10 +23,10 @@ data class SatDay(
     val slots: List<SatSlot> // 12 槽(00-02 ... 22-24)
 )
 
-/** One satellite, 6 days of state */
+/** One satellite, 3 days of state */
 data class SatStatus(
     val name: String,        // "AO-123_[FM]"
-    val days: List<SatDay>   // 6 天(新→旧)
+    val days: List<SatDay>   // 3 days (newest first)
 )
 
 /** Overall page parse result */

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/model/Settings.kt

@@ -42,6 +42,7 @@ data class RCSettings(
     val frequencyAddress: String,
     val frequencyPort: String,
     val frequencyFormat: String,
+    val frequencyOffsetHz: Long = 0L,
     val bluetoothRotatorState: Boolean,
     val bluetoothRotatorFormat: String,
     val bluetoothRotatorName: String,
@@ -66,10 +67,8 @@ data class OtherSettings(
 )
 
 data class DataSourcesSettings(
-    val useCustomTLE: Boolean,
-    val useCustomTransceivers: Boolean,
-    val tleUrl: String,
-    val transceiversUrl: String
+    val satelliteUrls: List<String>,
+    val transceiversUrls: List<String>
 )
 
 data class RadioControlSettings(

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/predict/CelestialComputer.kt

@@ -424,11 +424,15 @@ object CelestialComputer {
         }
         if (sunrise == 0.0) sunrise = daynum
 
-        // Phase 4: fast-forward through the day until sun drops back below threshold
-        daynum = sunrise
+        // Phase 4: fast-forward through the day until sun drops back below threshold.
+        // Start from just after sunrise (small offset) so the sun is clearly above
+        // the threshold. This prevents a bug where Phase 3 converges to a point
+        // slightly below -threshold, causing Phase 4 to skip and Phase 5 to converge
+        // to the same time as sunrise, producing identical sunrise/sunset times.
+        daynum = sunrise + 0.001
         sunPos = getSunPosition(observer, daynumToMillis(daynum))
         guard = 0
-        while (sunPos.elevation > -threshold && guard++ < 500) {
+        while (sunPos.elevation >= -threshold && guard++ < 500) {
             daynum += 0.008
             sunPos = getSunPosition(observer, daynumToMillis(daynum))
         }

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/source/Sources.kt

@@ -46,9 +46,11 @@ object Sources {
         "Classified" to "https://www.mmccants.org/tles/classfd.zip",
         "McCants" to "https://www.mmccants.org/tles/inttles.zip",
         "R4UAB" to "https://r4uab.ru/satonline.txt",
+        "ARISS" to "https://live.ariss.org/iss.txt",
         "Other" to "" // key for sats filter
     )
     val transceiversDataUrls = mapOf(
-        "SatNOGS" to "https://db.satnogs.org/api/transmitters/?format=json&status=active"
+        "SatNOGS" to "https://db.satnogs.org/api/transmitters/?format=json&status=active",
+        "R4UAB" to "https://r4uab.ru/transmitters.json"
     )
 }