feat(academic-periods): period selector, active period

API, holiday indicators; UI polish; bump version

Dashboard:

Add Syncfusion academic period dropdown next to group selector
Navigate scheduler to today's month/day within selected period year on change
Show adjacent holiday plan badge; keep "holidays in view" counter on the right
Compact dropdown widths for a tighter toolbar
Default blocking of scheduling on holidays; block entries styled like all-day; black text styling
API:

Add academic periods routes: list, get active, set active (POST), for_date
Register blueprint in wsgi
Holidays:

Support TXT/CSV upload; headerless TXT uses columns 2-4; region remains null
Docs:

Update shared Copilot instructions with academic periods endpoints and dashboard integration details

dashboard/public/program-info.json

@@ -1,6 +1,6 @@
 {
   "appName": "Infoscreen-Management",
-  "version": "2025.1.0-alpha.6",
+  "version": "2025.1.0-alpha.7",
   "copyright": "© 2025 Third-Age-Applications",
   "supportContact": "support@third-age-applications.com",
   "description": "Eine zentrale Verwaltungsoberfläche für digitale Informationsbildschirme.",
@@ -30,6 +30,18 @@
     "commitId": "8d1df7199cb7"
   },
   "changelog": [
+    {
+      "version": "2025.1.0-alpha.7",
+      "date": "2025-09-21",
+      "changes": [
+        "🧭 UI: Periode-Auswahl (Syncfusion) neben Gruppenauswahl; kompaktes Layout",
+        "✅ Anzeige: Abzeichen für vorhandenen Ferienplan + Zähler ‘Ferien im Blick’",
+        "🛠️ API: Endpunkte für akademische Perioden (list, active GET/POST, for_date)",
+        "📅 Scheduler: Standardmäßig keine Terminierung in Ferien; Block-Darstellung wie Ganztagesereignis; schwarze Textfarbe",
+        "📤 Ferien: Upload von TXT/CSV (headless TXT nutzt Spalten 2–4)",
+        "🔧 UX: Schalter in einer Reihe; Dropdown-Breiten optimiert"
+      ]
+    },
     {
       "version": "2025.1.0-alpha.6",
       "date": "2025-09-20",