fix: dynamic currency symbols and integrated datetime picker

- Replace all hardcoded prefix="$" with :prefix="getCurrencySymbol()"
  in Settings, Projects, and Invoices views
- Replace hardcoded ($) labels with dynamic currency symbol
- Extend AppDatePicker with showTime prop + hour/minute v-models
  for integrated date+time selection
- Simplify Entries.vue to use single AppDatePicker with showTime
  instead of separate hour/minute inputs

src/views/Settings.vue

@@ -155,7 +155,7 @@
             :min="0"
             :step="1"
             :precision="2"
-            prefix="$"
+            :prefix="getCurrencySymbol()"
             @update:model-value="saveSettings"
           />
         </div>
@@ -241,7 +241,7 @@ import { useSettingsStore } from '../stores/settings'
 import { useToastStore } from '../stores/toast'
 import AppNumberInput from '../components/AppNumberInput.vue'
 import AppSelect from '../components/AppSelect.vue'
-import { LOCALES, getCurrencies } from '../utils/locale'
+import { LOCALES, getCurrencies, getCurrencySymbol } from '../utils/locale'
 
 const settingsStore = useSettingsStore()
 const toastStore = useToastStore()