refactor: rename RDReaderView -> RDEpubReaderView, update pod config and docs

- Rename source module from RDReaderView to RDEpubReaderView
- Move all source files from Sources/RDReaderView/ to Sources/RDEpubReaderView/
- Update podspec: RDReaderView.podspec -> RDEpubReaderView.podspec
- Update Podfile, demo project, and CocoaPods config for new pod name
- Delete old RDReaderView pod support files from ReadViewDemo/Pods
- Add new RDEpubReaderView pod support files
- Update documentation (API ref, architecture, UML, conventions, etc.)
- Add FixedLayoutRotationTests
- Update .gitignore: exclude .DS_Store, manual unpack backups, _ssoft-output

Sources/RDEpubReaderView/ReaderView/Paging/RDEpubReaderSpreadResolver.swift

@@ -0,0 +1,74 @@
+
+import Foundation
+
+struct RDEpubReaderSpreadResolver {
+
+    func isFullScreenPage(
+        _ pageNum: Int,
+        landscapeDualPageEnabled: Bool,
+        isLandscape: Bool,
+        coverPageIndex: Int?
+    ) -> Bool {
+        guard landscapeDualPageEnabled, isLandscape, let coverIndex = coverPageIndex else { return false }
+        return pageNum == coverIndex
+    }
+
+    func dualPagePair(
+        for pageNum: Int,
+        totalPages: Int,
+        coverPageIndex: Int?
+    ) -> (left: Int, right: Int?) {
+        if let coverIndex = coverPageIndex {
+            if pageNum == coverIndex {
+                return (coverIndex, nil)
+            }
+            let adjustedIndex = pageNum - (coverIndex + 1)
+            let pairStart = coverIndex + 1 + (adjustedIndex / 2) * 2
+            let left = pairStart
+            let right = pairStart + 1 < totalPages ? pairStart + 1 : nil
+            return (left, right)
+        }
+
+        let left = (pageNum / 2) * 2
+        let right = left + 1 < totalPages ? left + 1 : nil
+        return (left, right)
+    }
+
+    func adjacentDualPage(
+        from pageNum: Int,
+        totalPages: Int,
+        coverPageIndex: Int?,
+        forward: Bool
+    ) -> Int? {
+        let pair = dualPagePair(for: pageNum, totalPages: totalPages, coverPageIndex: coverPageIndex)
+        if forward {
+            let nextStart = (pair.right ?? pair.left) + 1
+            return nextStart < totalPages ? nextStart : nil
+        }
+
+        let prevEnd = pair.left - 1
+        guard prevEnd >= 0 else { return nil }
+        return dualPagePair(for: prevEnd, totalPages: totalPages, coverPageIndex: coverPageIndex).left
+    }
+
+    func nextPage(
+        from currentPage: Int,
+        totalPages: Int,
+        pagesPerScreen: Int,
+        coverPageIndex: Int?,
+        forward: Bool
+    ) -> Int? {
+        if pagesPerScreen > 1 {
+            return adjacentDualPage(
+                from: currentPage,
+                totalPages: totalPages,
+                coverPageIndex: coverPageIndex,
+                forward: forward
+            )
+        }
+
+        let target = currentPage + (forward ? 1 : -1)
+        guard target >= 0, target < totalPages else { return nil }
+        return target
+    }
+}