fix(settings): force custom-source toggles off when legacy example.com URL present

Old installs that once enabled the custom TLE/transceiver toggles kept
the legacy "https://example.com/tle.txt" placeholder in preferences.
Under the new "toggle replaces the online-update default source"
semantics this pointed the All/SatNOGS fetch at a dead URL and broke
satellite updates after upgrading to 4.4.8.

Migration in getDataSourcesSettings(): example.com placeholders are
replaced by the real default URLs (Celestrak All / SatNOGS) and the
toggles are forced OFF unless a non-default, real user URL is set.
Also disable the reset (loop) icon buttons while their toggle is off.

Verified: core:data tests pass, settings + app compile. Version stays
4.4.8 (覆盖 per user).

core/data/src/main/java/com/rtbishop/look4sat/core/data/repository/SettingsRepo.kt

@@ -391,12 +391,20 @@ class SettingsRepo(
         _dataSourcesSettings.value = settings
     }
 
-    private fun getDataSourcesSettings(): DataSourcesSettings = DataSourcesSettings(
-        useCustomTLE = preferences.getBoolean(keyUseCustomTle, false),
-        useCustomTransceivers = preferences.getBoolean(keyUseCustomTransceivers, false),
-        tleUrl = preferences.getString(keyTleUrl, Sources.defaultTleUrl) ?: "",
-        transceiversUrl = preferences.getString(keyTransceiversUrl, Sources.defaultTransceiversUrl) ?: ""
-    )
+    private fun getDataSourcesSettings(): DataSourcesSettings {
+        // 4.4.8 修复: 旧版 example.com 占位 URL 视为未配置 -> 替换为真实默认 URL 且开关强制关闭,
+        // 否则在线更新的 All/SatNOGS 源会指向错误地址导致更新失败
+        val storedTleUrl = preferences.getString(keyTleUrl, Sources.defaultTleUrl) ?: Sources.defaultTleUrl
+        val storedTxUrl = preferences.getString(keyTransceiversUrl, Sources.defaultTransceiversUrl) ?: Sources.defaultTransceiversUrl
+        val tleUrl = if (storedTleUrl == "https://example.com/tle.txt") Sources.defaultTleUrl else storedTleUrl
+        val txUrl = if (storedTxUrl == "https://example.com/radio.json") Sources.defaultTransceiversUrl else storedTxUrl
+        return DataSourcesSettings(
+            useCustomTLE = preferences.getBoolean(keyUseCustomTle, false) && tleUrl != Sources.defaultTleUrl,
+            useCustomTransceivers = preferences.getBoolean(keyUseCustomTransceivers, false) && txUrl != Sources.defaultTransceiversUrl,
+            tleUrl = tleUrl,
+            transceiversUrl = txUrl
+        )
+    }
     //endregion
 
     //region # Radio control settings

feature/settings/src/main/java/com/rtbishop/look4sat/feature/settings/SettingsDialog.kt

@@ -208,7 +208,10 @@ fun DataSourcesDialog(
                 modifier = Modifier.fillMaxWidth(),
                 enabled = isEnabledCustomTle.value,
                 trailingIcon = {
-                    IconButton(onClick = { urlTle.value = Sources.defaultTleUrl }) {
+                    IconButton(
+                        onClick = { urlTle.value = Sources.defaultTleUrl },
+                        enabled = isEnabledCustomTle.value
+                    ) {
                         Icon(
                             painter = painterResource(id = R.drawable.ic_reset),
                             contentDescription = stringResource(id = R.string.prefs_data_reset_url)
@@ -245,7 +248,10 @@ fun DataSourcesDialog(
                 modifier = Modifier.fillMaxWidth(),
                 enabled = isEnabledCustomTransceivers.value,
                 trailingIcon = {
-                    IconButton(onClick = { urlTransceivers.value = Sources.defaultTransceiversUrl }) {
+                    IconButton(
+                        onClick = { urlTransceivers.value = Sources.defaultTransceiversUrl },
+                        enabled = isEnabledCustomTransceivers.value
+                    ) {
                         Icon(
                             painter = painterResource(id = R.drawable.ic_reset),
                             contentDescription = stringResource(id = R.string.prefs_data_reset_url)