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).

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)