fix: address code review findings across sync, tasks, and UI (#6339)

- fix(tasks): preserve selectAllTasks memoization by only filtering when
  undefined entities exist, avoiding new array allocation on every call
- fix(sync): replace mutable ARGON2_PARAMS export with getter/setter to
  prevent test pollution across spec files
- fix(sync): convert tag-task-page from async pipe to toSignal pattern
  to fix OnPush change detection after bulk sync state updates
- fix(sync): remove E2E navigation workarounds that masked the rendering
  bug now fixed by the toSignal conversion
- fix(sync): add clarifying comments for archive-wins sibling conflict
  resolution and waitForSyncWindow switchMap concurrency semantics
- fix(ios): add hex preview of first 16 bytes to WebDAV UTF-8 decode
  error for easier debugging
- docs: add JSDoc to getDiffInWeeks noting negative diff behavior

https://claude.ai/code/session_01Y51QDFEdvrJ9VVgp9XfWLJ

Co-authored-by: Claude <noreply@anthropic.com>

ios/App/App/WebDavHttpPlugin.swift

@@ -81,7 +81,8 @@ public class WebDavHttpPlugin: CAPPlugin, CAPBridgedPlugin {
             let bodyString: String
             if let responseData = responseData, !responseData.isEmpty {
                 guard let decoded = String(data: responseData, encoding: .utf8) else {
-                    call.reject("Failed to decode response as UTF-8 (\(responseData.count) bytes)", "DECODE_ERROR")
+                    let preview = responseData.prefix(16).map { String(format: "%02x", $0) }.joined(separator: " ")
+                    call.reject("Failed to decode response as UTF-8 (\(responseData.count) bytes, first bytes: \(preview))", "DECODE_ERROR")
                     return
                 }
                 bodyString = decoded