fix: transponder filters - mutual exclusion and beacon-free fallback

Two correctness fixes for the FM/Linear/SSTV filters:

1. Satellite type picker: virtual transponder types (AMSAT Live FM,
   AMSAT Live Linear, Live SSTV) are now mutually exclusive with the
   regular TLE-source types - ticking a virtual type clears Amateur/
   CubeSat/etc and vice versa, so selecting 'AMSAT Live FM' no longer
   unions in hundreds of non-transponder satellites. Virtual types
   still combine with each other. Also: an empty virtual-type resolve
   now yields an empty list instead of falling back to 'show all'.

2. Mutual-match fallback: when the AMSAT lists are empty (first run /
   sync failure) the DB mode filter used downlinkMode alone, so any
   downlink-only beacon sharing a mode label was misclassified
   (ISS/IO-86 CW beacons into Linear, FO-29's FM Digitalker into FM).
   New getIdsWithModesAndUplink() requires uplinkLow IS NOT NULL,
   matching real transponders only. SSTV filter keeps the old query
   (SSTV sats are often downlink-only).

Shared virtual-type names moved to Sources.virtualTypeNames.

core/domain/src/main/java/com/rtbishop/look4sat/core/domain/repository/ISatelliteRepo.kt

@@ -70,4 +70,9 @@ interface ISatelliteRepo {
      *  Empty modes -> empty result; used to filter the mutual-match satellite
      *  set to transponder satellites (FM voice / linear). */
     suspend fun getSatelliteIdsWithModes(modes: List<String>): List<Int>
+
+    /** Like [getSatelliteIdsWithModes] but only matches records with an uplink
+     *  (real transponders), excluding downlink-only beacons/telemetry that share
+     *  the same mode label. Used by the FM/Linear fallback filter. */
+    suspend fun getSatelliteIdsWithModesAndUplink(modes: List<String>): List<Int>
 }

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

@@ -29,6 +29,7 @@ interface ILocalSource {
     suspend fun insertEntries(entries: List<OrbitalData>)
     suspend fun deleteEntries()
     suspend fun getIdsWithModes(modes: List<String>): List<Int>
+    suspend fun getIdsWithModesAndUplink(modes: List<String>): List<Int>
     suspend fun getRadiosTotal(): Int
     suspend fun getRadiosWithId(id: Int): List<SatRadio>
     suspend fun insertRadios(radios: List<SatRadio>, isCustom: Boolean = false)

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

@@ -62,4 +62,10 @@ object Sources {
         "FM" to "https://www.amsat.org/live-fm-satellites/",
         "Linear" to "https://www.amsat.org/live-linear-satellites/"
     )
+
+    /** Virtual satellite-selection types: transponder/activity filters shown
+     *  at the top of the type picker. They resolve to live lists (AMSAT pages
+     *  or mode=SSTV radios) instead of persisted per-type IDs, and are
+     *  mutually exclusive with the regular TLE-source types in the picker. */
+    val virtualTypeNames = listOf("AMSAT Live FM", "AMSAT Live Linear", "Live SSTV")
 }