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/Invoices.vue

@@ -168,13 +168,13 @@
             />
           </div>
           <div>
-            <label class="block text-[0.6875rem] text-text-tertiary uppercase tracking-[0.08em] mb-1.5">Discount ($)</label>
+            <label class="block text-[0.6875rem] text-text-tertiary uppercase tracking-[0.08em] mb-1.5">Discount ({{ getCurrencySymbol() }})</label>
             <AppNumberInput
               v-model="createForm.discount"
               :min="0"
               :step="1"
               :precision="2"
-              prefix="$"
+              :prefix="getCurrencySymbol()"
             />
           </div>
         </div>
@@ -339,7 +339,7 @@ import { useInvoicesStore, type Invoice } from '../stores/invoices'
 import { useClientsStore } from '../stores/clients'
 import { useToastStore } from '../stores/toast'
 import { generateInvoicePdf } from '../utils/invoicePdf'
-import { formatDate, formatCurrency } from '../utils/locale'
+import { formatDate, formatCurrency, getCurrencySymbol } from '../utils/locale'
 
 const invoicesStore = useInvoicesStore()
 const clientsStore = useClientsStore()