feat(06-01): add TemplatePage, routing, sidebar nav, and i18n translations

- Create TemplatePage with add form (category/tier/amount), items table, and empty state
- Add /template route to App.tsx with TemplatePage component
- Add Template nav item to sidebar (between Categories and Settings)
- Add template and nav.template i18n keys for EN and DE
- Fix unused import in useTemplate hook

frontend/src/i18n/de.json

@@ -5,6 +5,7 @@
   "nav": {
     "dashboard": "Dashboard",
     "categories": "Kategorien",
+    "template": "Vorlage",
     "settings": "Einstellungen",
     "logout": "Abmelden"
   },
@@ -74,6 +75,21 @@
     "profile": "Profil",
     "save": "Speichern"
   },
+  "template": {
+    "title": "Monatliche Vorlage",
+    "addItem": "Eintrag hinzufuegen",
+    "category": "Kategorie",
+    "tier": "Typ",
+    "fixed": "Fest",
+    "variable": "Variabel",
+    "oneOff": "Einmalig",
+    "amount": "Betrag",
+    "actions": "Aktionen",
+    "noItems": "Noch keine Vorlageneintraege",
+    "noItemsHint": "Fuegen Sie feste und variable Eintraege hinzu, um Ihre monatliche Budgetvorlage zu definieren.",
+    "selectCategory": "Kategorie auswaehlen",
+    "selectTier": "Typ auswaehlen"
+  },
   "common": {
     "save": "Speichern",
     "cancel": "Abbrechen",

frontend/src/i18n/en.json

@@ -5,6 +5,7 @@
   "nav": {
     "dashboard": "Dashboard",
     "categories": "Categories",
+    "template": "Template",
     "settings": "Settings",
     "logout": "Logout"
   },
@@ -74,6 +75,21 @@
     "profile": "Profile",
     "save": "Save"
   },
+  "template": {
+    "title": "Monthly Template",
+    "addItem": "Add Item",
+    "category": "Category",
+    "tier": "Tier",
+    "fixed": "Fixed",
+    "variable": "Variable",
+    "oneOff": "One-off",
+    "amount": "Amount",
+    "actions": "Actions",
+    "noItems": "No template items yet",
+    "noItemsHint": "Add fixed and variable items to define your monthly budget template.",
+    "selectCategory": "Select category",
+    "selectTier": "Select tier"
+  },
   "common": {
     "save": "Save",
     "cancel": "Cancel",