Harden iOS app with audit fixes, UI consistency, and sheet race condition fixes

Applies verified fixes from deep audit (concurrency, performance, security,
accessibility), standardizes CRUD form buttons to Add/Save pattern, removes
.drawingGroup() that broke search bar TextFields, and converts vulnerable
.sheet(isPresented:) + if-let patterns to safe presentation to prevent
blank white modals.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

iosApp/iosApp/Localizable.xcstrings

@@ -107,10 +107,6 @@
     },
     "$" : {
 
-    },
-    "$%@" : {
-      "comment" : "A label displaying the cost of a task. The argument is the cost of the task.",
-      "isCommentAutoGenerated" : true
     },
     "000000" : {
       "comment" : "A placeholder text for a 6-digit code field.",
@@ -316,8 +312,8 @@
       "comment" : "An alert message displayed when the user taps the \"Archive\" button on a task. It confirms that the user intends to archive the task and provides a hint that the task can be restored later.",
       "isCommentAutoGenerated" : true
     },
-    "Are you sure you want to cancel this task? This action cannot be undone." : {
-      "comment" : "An alert message displayed when a user taps the \"Cancel Task\" button in the task details view. It confirms that the user intends to cancel the task and warns them that the action cannot be undone.",
+    "Are you sure you want to cancel this task? You can undo this later." : {
+      "comment" : "An alert message displayed when a user taps the \"Cancel Task\" button in a task list. It confirms that the user intends to cancel the task and provides a way to undo the action.",
       "isCommentAutoGenerated" : true
     },
     "Are you sure you want to remove %@ from this residence?" : {
@@ -4298,6 +4294,71 @@
       "comment" : "A description of how long the verification code is valid for.",
       "isCommentAutoGenerated" : true
     },
+    "common_add" : {
+      "extractionState" : "manual",
+      "localizations" : {
+        "de" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Hinzufügen"
+          }
+        },
+        "en" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Add"
+          }
+        },
+        "es" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Agregar"
+          }
+        },
+        "fr" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Ajouter"
+          }
+        },
+        "it" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Aggiungi"
+          }
+        },
+        "ja" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "追加"
+          }
+        },
+        "ko" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "추가"
+          }
+        },
+        "nl" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Toevoegen"
+          }
+        },
+        "pt" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "Adicionar"
+          }
+        },
+        "zh" : {
+          "stringUnit" : {
+            "state" : "translated",
+            "value" : "添加"
+          }
+        }
+      }
+    },
     "common_back" : {
       "extractionState" : "manual",
       "localizations" : {