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/EPUBUI/String+RDEPUB.swift

@@ -0,0 +1,17 @@
+import Foundation
+import CryptoKit
+
+extension String {
+
+    /// trim 后空字符串返回 nil
+    var rd_nilIfEmpty: String? {
+        let trimmed = trimmingCharacters(in: .whitespacesAndNewlines)
+        return trimmed.isEmpty ? nil : trimmed
+    }
+
+    /// SHA256 hex 摘要
+    var rd_sha256Hex: String {
+        let digest = SHA256.hash(data: Data(self.utf8))
+        return digest.map { String(format: "%02x", $0) }.joined()
+    }
+}