feat(ios): implement getContentCacheById, getLatestContentCache, and saveContentCache methods

Implemented content cache access methods using Core Data:

getContentCacheById():
- Returns content cache by ID or latest if ID not provided
- Uses Core Data fetch with predicate for ID lookup
- Returns null if cache not found
- Matches Android getContentCacheById method

getLatestContentCache():
- Returns latest content cache entry
- Delegates to getContentCacheById with no ID
- Matches Android getLatestContentCache method

saveContentCache():
- Saves content to cache in Core Data
- Auto-generates ID if not provided (cache_timestamp)
- Converts payload string to Data for storage
- Stores fetchedAt, ttlSeconds, payload, and meta
- Returns saved cache object

iOS Adaptations:
- Uses Core Data ContentCache entity
- Payload stored as Data (from JSON string)
- Timestamp conversion (Date to milliseconds)
- Error handling for invalid payload data

Progress: 47/52 methods implemented (90% complete)

ios/Plugin/DailyNotificationPlugin.swift

@@ -1333,6 +1333,143 @@ public class DailyNotificationPlugin: CAPPlugin {
         }
     }
     
+    /**
+     * Get content cache by ID
+     * 
+     * Returns content cache by ID, or latest if ID not provided.
+     * 
+     * Equivalent to Android's getContentCacheById method.
+     */
+    @objc func getContentCacheById(_ call: CAPPluginCall) {
+        let options = call.getObject("options")
+        let id = options?["id"] as? String
+        
+        print("DNP-PLUGIN: Getting content cache: id=\(id ?? "latest")")
+        
+        Task {
+            do {
+                let context = persistenceController.container.viewContext
+                let request: NSFetchRequest<ContentCache> = ContentCache.fetchRequest()
+                
+                if let cacheId = id {
+                    request.predicate = NSPredicate(format: "id == %@", cacheId)
+                } else {
+                    request.sortDescriptors = [NSSortDescriptor(keyPath: \ContentCache.fetchedAt, ascending: false)]
+                    request.fetchLimit = 1
+                }
+                
+                let results = try context.fetch(request)
+                
+                if let cache = results.first {
+                    let payload = try JSONSerialization.jsonObject(with: cache.payload!) as? [String: Any] ?? [:]
+                    
+                    let result: [String: Any] = [
+                        "id": cache.id ?? "",
+                        "fetchedAt": Int64((cache.fetchedAt?.timeIntervalSince1970 ?? 0) * 1000),
+                        "ttlSeconds": cache.ttlSeconds,
+                        "payload": payload,
+                        "meta": cache.meta ?? ""
+                    ]
+                    
+                    DispatchQueue.main.async {
+                        call.resolve(result)
+                    }
+                } else {
+                    DispatchQueue.main.async {
+                        call.resolve(["contentCache": NSNull()])
+                    }
+                }
+            } catch {
+                print("DNP-PLUGIN: Failed to get content cache: \(error)")
+                DispatchQueue.main.async {
+                    call.reject("Failed to get content cache: \(error.localizedDescription)")
+                }
+            }
+        }
+    }
+    
+    /**
+     * Get latest content cache
+     * 
+     * Returns the latest content cache entry.
+     * 
+     * Equivalent to Android's getLatestContentCache method.
+     */
+    @objc func getLatestContentCache(_ call: CAPPluginCall) {
+        // Delegate to getContentCacheById with no ID (returns latest)
+        let options: [String: Any] = [:]
+        call.options = options
+        getContentCacheById(call)
+    }
+    
+    /**
+     * Save content cache
+     * 
+     * Saves content to cache in Core Data.
+     * 
+     * Equivalent to Android's saveContentCache method.
+     */
+    @objc func saveContentCache(_ call: CAPPluginCall) {
+        guard let contentJson = call.getObject("content") else {
+            call.reject("Content data is required")
+            return
+        }
+        
+        guard let payloadString = contentJson["payload"] as? String else {
+            call.reject("Payload is required")
+            return
+        }
+        
+        guard let ttlSeconds = contentJson["ttlSeconds"] as? Int else {
+            call.reject("TTL seconds is required")
+            return
+        }
+        
+        let id = contentJson["id"] as? String ?? "cache_\(Int64(Date().timeIntervalSince1970 * 1000))"
+        let meta = contentJson["meta"] as? String
+        
+        print("DNP-PLUGIN: Saving content cache: id=\(id)")
+        
+        Task {
+            do {
+                let context = persistenceController.container.viewContext
+                
+                // Convert payload string to Data
+                guard let payloadData = payloadString.data(using: .utf8) else {
+                    throw NSError(domain: "DailyNotificationPlugin", code: 1, userInfo: [NSLocalizedDescriptionKey: "Invalid payload data"])
+                }
+                
+                let cache = ContentCache(context: context)
+                cache.id = id
+                cache.fetchedAt = Date()
+                cache.ttlSeconds = Int32(ttlSeconds)
+                cache.payload = payloadData
+                cache.meta = meta
+                
+                try context.save()
+                
+                let result: [String: Any] = [
+                    "id": id,
+                    "fetchedAt": Int64(Date().timeIntervalSince1970 * 1000),
+                    "ttlSeconds": ttlSeconds,
+                    "payload": try JSONSerialization.jsonObject(with: payloadData) as? [String: Any] ?? [:],
+                    "meta": meta ?? ""
+                ]
+                
+                print("DNP-PLUGIN: Content cache saved successfully")
+                
+                DispatchQueue.main.async {
+                    call.resolve(result)
+                }
+            } catch {
+                print("DNP-PLUGIN: Failed to save content cache: \(error)")
+                DispatchQueue.main.async {
+                    call.reject("Failed to save content cache: \(error.localizedDescription)")
+                }
+            }
+        }
+    }
+    
     /**
      * Get power state
      *