feat: add checkbox to include consumption from today until planner start date (#98)

- Add 'Include consumption from today until start date' checkbox to planner
- When checked, usage calculation starts from today instead of max(today, startDate)
- Persist checkbox state in localStorage per user
- Add i18n translations (EN + DE)
- Update planner tests to use dynamic future dates

frontend/src/i18n/de.json

@@ -176,6 +176,7 @@
     "badge": "Vorrat planen",
     "from": "Von",
     "until": "Bis",
+    "includeUntilStart": "Verbrauch von heute bis Startdatum einrechnen",
     "calculate": "Berechnen",
     "calculating": "Wird berechnet...",
     "sendEmail": "📧 Per E-Mail senden",

frontend/src/i18n/en.json

@@ -176,6 +176,7 @@
     "badge": "Plan your supply",
     "from": "From",
     "until": "Until",
+    "includeUntilStart": "Include consumption from today until start date",
     "calculate": "Calculate",
     "calculating": "Calculating...",
     "sendEmail": "📧 Send via Email",