refactor(dm): tighten visibility of internal-only paging helpers

- BackwardRelayPager.floorFor was public but only ever called inside the
  pager (and its same-module test) — narrow to internal.
- RelayReachMarker composable was public but only rendered by
  RelayWindowLimitMarkers in the same file; the public entry points are
  RelayWindowLimitMarkers/Sentinels — make it private.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

commons/src/commonMain/kotlin/com/vitorpamplona/amethyst/commons/ui/feeds/RelayReachMarker.kt

@@ -196,7 +196,7 @@ fun RelayWindowLimitMarkers(
  * Reads e.g. "Relay sync: ✓ 8 · ↓ 1" or "Relay sync: ↓ nostr.wine".
  */
 @Composable
-fun RelayReachMarker(entries: List<RelayReach>) {
+private fun RelayReachMarker(entries: List<RelayReach>) {
     if (entries.isEmpty()) return
 
     Row(

quartz/src/jvmAndroid/kotlin/com/vitorpamplona/quartz/nip01Core/relay/client/paging/BackwardRelayPager.kt

@@ -132,7 +132,7 @@ class BackwardRelayPager<K>(
     val relayProgress: StateFlow<Map<NormalizedRelayUrl, RelayPagingProgress>> = _relayProgress.asStateFlow()
 
     /** The session-pinned floor for [key] — where its paging starts (just below the live tail). */
-    fun floorFor(key: K): Long = pinnedFloor.getOrPut(key) { TimeUtils.now() - liveTailSeconds }
+    internal fun floorFor(key: K): Long = pinnedFloor.getOrPut(key) { TimeUtils.now() - liveTailSeconds }
 
     // --- Filter building support: the caller assembles the actual REQ from these. ---