style: replace em dashes with hyphens throughout codebase

Replace all — with - in all source files (JS, CSS, HTML, JSON,
Markdown) for consistency and readability.

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

public/locales/en.json

@@ -21,7 +21,7 @@
     "errorOccurred": "Something went wrong.",
     "unexpectedError": "An unexpected error occurred.",
     "errorGeneric": "An error occurred.",
-    "updateAvailable": "Update available — reload the page to get the latest version.",
+    "updateAvailable": "Update available - reload the page to get the latest version.",
     "titleRequired": "Title is required",
     "nameRequired": "Name is required",
     "contentRequired": "Content is required",
@@ -82,7 +82,7 @@
     "title": "Tasks",
     "newTask": "New Task",
     "editTask": "Edit Task",
-    "emptyTitle": "No tasks — all done?",
+    "emptyTitle": "No tasks - all done?",
     "emptyDescription": "Create new tasks with the + button.",
     "titleLabel": "Title *",
     "titlePlaceholder": "What needs to be done?",
@@ -93,7 +93,7 @@
     "dueDateLabel": "Due date",
     "dueTimeLabel": "Time",
     "assignedLabel": "Assigned to",
-    "assignedNobody": "— Nobody —",
+    "assignedNobody": "- Nobody -",
     "statusLabel": "Status",
     "priorityUrgent": "Urgent",
     "priorityHigh": "High",
@@ -259,7 +259,7 @@
     "locationLabel": "Location",
     "locationPlaceholder": "Optional",
     "assignedLabel": "Assigned to",
-    "assignedNobody": "— Nobody —",
+    "assignedNobody": "- Nobody -",
     "colorLabel": "Color",
     "descriptionLabel": "Description",
     "descriptionPlaceholder": "Optional…",
@@ -428,7 +428,7 @@
     "savedToast": "Entry saved",
     "deletedToast": "Entry deleted",
     "loadError": "Budget could not be loaded.",
-    "trendNeutral": "— same as {{month}}",
+    "trendNeutral": "- same as {{month}}",
     "validAmountRequired": "Please enter a valid amount",
     "dateRequired": "Date is required",
     "catFood": "Groceries",