feat: Phase 2 – Budget-Engine + Direktzugriff (http://IP:Port)

Budget:
- Modelle + Migration 0003: budget_template_lines, planned_income_lines,
  budget_periods, budget_period_lines.
- services/budget: Perioden-Grenzen (einstellbarer Starttag, Label nach Endmonat),
  Standard-Vorlage vs. Monats-Override (Snapshot-on-Customize), Soll/Ist inkl.
  budgetierter Sparen-Transfers, geplante Einnahmen (Soll/Ist).
- routers/budgets: Vorlage, geplante Einnahmen (CRUD), Monats-Soll/Ist,
  Monats-Override, Zurücksetzen. pytest: Perioden, Soll/Ist, Override/Reset, Einnahmen.
- Frontend: Budget-Seite (Monat + Standard-Budget), Fortschrittsbalken grün/rot,
  Monats-Navigation, editierbare Soll-Beträge; Sparen-Option im Transfer-Formular.

Deployment-Fix (Nutzer-Anforderung: http://IP:Port muss funktionieren):
- Dienst bindet an APP_BIND_HOST=0.0.0.0 (direkt im LAN erreichbar).
- APP_COOKIE_SECURE=false als Standard (sonst kein Login über reines HTTP);
  für reinen HTTPS-Betrieb umstellbar. Doku + install.sh entsprechend angepasst.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

web/src/locales/en.json

@@ -150,6 +150,29 @@
     "allTypes": "All types",
     "deleteConfirm": "Delete this transaction?",
     "amountRequired": "Please enter an amount.",
-    "accountRequired": "Please choose an account."
+    "accountRequired": "Please choose an account.",
+    "budgetAsSavings": "Count as savings in the budget",
+    "budgetCategory": "Budget category"
+  },
+  "budget": {
+    "title": "Budget",
+    "monthMode": "Month",
+    "templateMode": "Standard budget",
+    "income": "Income",
+    "expenses": "Expenses",
+    "planned": "Planned",
+    "totalIncome": "Total income",
+    "totalExpense": "Total expenses",
+    "reset": "Reset to standard",
+    "resetTitle": "Reset month",
+    "resetConfirm": "Reset this month to the standard budget? This month's adjustments will be lost.",
+    "templateHint": "The standard budget applies to every month until you adjust a month individually.",
+    "addIncome": "Planned income",
+    "editIncome": "Edit income",
+    "noIncome": "No planned income yet.",
+    "deleteIncomeConfirm": "Delete this planned income?",
+    "incomeLabel": "Label",
+    "incomeCategory": "Category",
+    "targetAccount": "Target account"
   }
 }