Add diagnostic logs for total pages not updating investigation

Add RDEPUBBackgroundTrace.log at key decision points in the
reconciliation pipeline to trace why pageMap updates get rejected:

1. refreshBookPageMapInPlace — logs when a full pageMap update is enqueued
2. evaluateTakeover — logs when keepCurrentWindow is returned due to:
   - jumpSession coverage ratio < 0.8
   - adjacent coverage missing (hasPrev/hasNext)
   - renderSignature mismatch
3. evaluateFullPageMapTakeover — logs when keepCurrentWindow is returned due to:
   - currentSpineIndex not in candidate chapters
   - adjacent coverage missing
4. commitPendingPageMapUpdate — logs when keepCurrentWindow decision is
   applied and pending update is removed from queue

Also fix unused variable warning for currentPageNumber in extendPartial case.

Co-Authored-By: Claude <noreply@anthropic.com>

Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBPresentationRuntime.swift

@@ -56,6 +56,10 @@ final class RDEPUBPresentationRuntime {
 
     func refreshBookPageMapInPlace(_ bookPageMap: RDEPUBBookPageMap) {
         navigationStateMachine.transition(to: .reconcilingFullMap)
+        RDEPUBBackgroundTrace.log(
+            "Reconciliation",
+            "refreshBookPageMapInPlace: enqueued reconcileFullMap chapters=\(bookPageMap.totalChapters) pages=\(bookPageMap.totalPages)"
+        )
         enqueuePendingPageMapUpdate(
             RDEPUBPendingPageMapUpdate(
                 pageMap: bookPageMap,
@@ -225,6 +229,10 @@ final class RDEPUBPresentationRuntime {
 
             switch decision {
             case .keepCurrentWindow:
+                RDEPUBBackgroundTrace.log(
+                    "Reconciliation",
+                    "commitPendingPageMapUpdate: keepCurrentWindow — removed pending update, totalPages=\(update.pageMap.totalPages)"
+                )
                 removePendingPageMapUpdate(at: index)
                 return false
 
@@ -238,7 +246,7 @@ final class RDEPUBPresentationRuntime {
                 return false
             }
 
-        case .extendPartial(let currentPageNumber, let currentLocation):
+        case .extendPartial(_, let currentLocation):
             removePendingPageMapUpdate(at: index)
             applyPageMapToLiveModel(update.pageMap, source: update.source)
             if let currentLocation,