feat: 2026.1.0-alpha.16 – dashboard banner refactor, period auto-activation, text & docs

Dashboard (dashboard/src/dashboard.tsx, settings.tsx, apiAcademicPeriods.ts):
- Refactor loadHolidayStatus to useCallback with stable empty-deps reference;
  removes location.pathname dependency that caused overlapping API calls at mount
  and left the banner unresolved via request-sequence cancellation
- Add key prop derived from severity:text to Syncfusion MessageComponent to force
  remount on state change, fixing stale banner that ignored React prop/children updates
- Correct German transliterated text to proper Umlauts throughout visible UI strings
  (fuer -> für, oe -> ö, ae -> ä etc. across dashboard and settings views)

Backend (server/init_academic_periods.py):
- Refactor to idempotent two-phase flow: seed default periods only when table is
  empty; on every run activate exactly the non-archived period covering date.today()
- Enforces single-active invariant by deactivating all periods before promoting match
- Emits explicit warning when no period covers current date instead of doing nothing

Deployment (docker-compose.prod.yml):
- Add init_academic_periods.py to server startup chain after migrations and defaults;
  eliminates manual post-deploy step to set an active academic period

Release docs:
- program-info.json: bump to 2026.1.0-alpha.16; fix JSON parse error caused by
  typographic curly quotes in the new changelog entry
- TECH-CHANGELOG.md: detailed alpha.16 section with root-cause motivation for both
  dashboard refactoring decisions (unstable callback ref + Syncfusion stale render)
- DEV-CHANGELOG.md: document dashboard refactor, Syncfusion key fix, Umlaut changes,
  and program-info JSON regression and fix
- README.md: add Latest Release Highlights section for alpha.16
- .github/copilot-instructions.md: sync file map, prod bootstrap note, backend and
  frontend pattern additions for academic period init and Syncfusion remount pattern

server/init_academic_periods.py

@@ -1,7 +1,11 @@
 #!/usr/bin/env python3
 """
-Erstellt Standard-Schuljahre für österreichische Schulen
-Führe dieses Skript nach der Migration aus, um Standard-Perioden zu erstellen.
+Erstellt Standard-Schuljahre und setzt automatisch die aktive Periode.
+
+Dieses Skript ist idempotent:
+- Wenn keine Perioden existieren, werden Standard-Perioden erstellt.
+- Danach wird (bei jedem Lauf) die nicht-archivierte Periode aktiviert,
+  die das heutige Datum abdeckt.
 """
 
 from datetime import date
@@ -11,54 +15,94 @@ import sys
 sys.path.append('/workspace')
 
 
+def _create_default_periods_if_missing(session):
+    """Erstellt Standard-Schuljahre nur dann, wenn noch keine Perioden existieren."""
+    existing = session.query(AcademicPeriod).first()
+    if existing:
+        print("Academic periods already exist. Skipping creation.")
+        return False
+
+    periods = [
+        {
+            'name': 'Schuljahr 2024/25',
+            'display_name': 'SJ 24/25',
+            'start_date': date(2024, 9, 2),
+            'end_date': date(2025, 7, 4),
+            'period_type': AcademicPeriodType.schuljahr,
+            'is_active': False
+        },
+        {
+            'name': 'Schuljahr 2025/26',
+            'display_name': 'SJ 25/26',
+            'start_date': date(2025, 9, 1),
+            'end_date': date(2026, 7, 3),
+            'period_type': AcademicPeriodType.schuljahr,
+            'is_active': False
+        },
+        {
+            'name': 'Schuljahr 2026/27',
+            'display_name': 'SJ 26/27',
+            'start_date': date(2026, 9, 7),
+            'end_date': date(2027, 7, 2),
+            'period_type': AcademicPeriodType.schuljahr,
+            'is_active': False
+        }
+    ]
+
+    for period_data in periods:
+        period = AcademicPeriod(**period_data)
+        session.add(period)
+
+    session.flush()
+    print(f"Successfully created {len(periods)} academic periods")
+    return True
+
+
+def _activate_period_for_today(session):
+    """Aktiviert genau eine Periode: die Periode, die heute abdeckt."""
+    today = date.today()
+
+    period_for_today = (
+        session.query(AcademicPeriod)
+        .filter(
+            AcademicPeriod.is_archived == False,
+            AcademicPeriod.start_date <= today,
+            AcademicPeriod.end_date >= today,
+        )
+        .order_by(AcademicPeriod.start_date.desc())
+        .first()
+    )
+
+    # Immer zunächst alle aktiven Perioden deaktivieren, um den Zustand konsistent zu halten.
+    session.query(AcademicPeriod).filter(AcademicPeriod.is_active == True).update(
+        {AcademicPeriod.is_active: False},
+        synchronize_session=False,
+    )
+
+    if period_for_today:
+        period_for_today.is_active = True
+        print(
+            f"Activated academic period for today ({today}): {period_for_today.name} "
+            f"[{period_for_today.start_date} - {period_for_today.end_date}]"
+        )
+    else:
+        print(
+            f"WARNING: No academic period covers today ({today}). "
+            "All periods remain inactive."
+        )
+
+
 def create_default_academic_periods():
-    """Erstellt Standard-Schuljahre für österreichische Schulen"""
+    """Erstellt Standard-Perioden (falls nötig) und setzt aktive Periode für heute."""
     session = Session()
 
     try:
-        # Prüfe ob bereits Perioden existieren
-        existing = session.query(AcademicPeriod).first()
-        if existing:
-            print("Academic periods already exist. Skipping creation.")
-            return
-
-        # Standard Schuljahre erstellen
-        periods = [
-            {
-                'name': 'Schuljahr 2024/25',
-                'display_name': 'SJ 24/25',
-                'start_date': date(2024, 9, 2),
-                'end_date': date(2025, 7, 4),
-                'period_type': AcademicPeriodType.schuljahr,
-                'is_active': True  # Aktuelles Schuljahr
-            },
-            {
-                'name': 'Schuljahr 2025/26',
-                'display_name': 'SJ 25/26',
-                'start_date': date(2025, 9, 1),
-                'end_date': date(2026, 7, 3),
-                'period_type': AcademicPeriodType.schuljahr,
-                'is_active': False
-            },
-            {
-                'name': 'Schuljahr 2026/27',
-                'display_name': 'SJ 26/27',
-                'start_date': date(2026, 9, 7),
-                'end_date': date(2027, 7, 2),
-                'period_type': AcademicPeriodType.schuljahr,
-                'is_active': False
-            }
-        ]
-
-        for period_data in periods:
-            period = AcademicPeriod(**period_data)
-            session.add(period)
-
+        _create_default_periods_if_missing(session)
+        _activate_period_for_today(session)
         session.commit()
-        print(f"Successfully created {len(periods)} academic periods")
 
         # Zeige erstellte Perioden
-        for period in session.query(AcademicPeriod).all():
+        for period in session.query(AcademicPeriod).order_by(AcademicPeriod.start_date.asc()).all():
             status = "AKTIV" if period.is_active else "inaktiv"
             print(
                 f"  - {period.name} ({period.start_date} - {period.end_date}) [{status}]")