feat: Add academic periods system for educational institutions

- Add AcademicPeriod model with support for schuljahr/semester/trimester
- Extend Event and EventMedia models with optional academic_period_id
- Create Alembic migration (8d1df7199cb7) for academic periods system
- Add init script for Austrian school year defaults (2024/25-2026/27)
- Maintain full backward compatibility for existing events/media
- Update program-info.json to version 2025.1.0-alpha.6

Database changes:
- New academic_periods table with unique name constraint
- Foreign key relationships with proper indexing
- Support for multiple period types with single active period

This lays the foundation for period-based organization of events
and media content, specifically designed for school environments
with future extensibility for universities.

server/routes/holidays.py

@@ -0,0 +1,109 @@
+from flask import Blueprint, request, jsonify
+from server.database import Session
+from models.models import SchoolHoliday
+from datetime import datetime
+import csv
+import io
+
+holidays_bp = Blueprint("holidays", __name__, url_prefix="/api/holidays")
+
+
+@holidays_bp.route("", methods=["GET"])
+def list_holidays():
+    session = Session()
+    region = request.args.get("region")
+    q = session.query(SchoolHoliday)
+    if region:
+        q = q.filter(SchoolHoliday.region == region)
+    rows = q.order_by(SchoolHoliday.start_date.asc()).all()
+    data = [r.to_dict() for r in rows]
+    session.close()
+    return jsonify({"holidays": data})
+
+
+@holidays_bp.route("/upload", methods=["POST"])
+def upload_holidays():
+    """
+    Accepts a CSV file upload (multipart/form-data) with columns like:
+    name,start_date,end_date,region
+    Dates can be in ISO (YYYY-MM-DD) or common European format (DD.MM.YYYY).
+    """
+    if "file" not in request.files:
+        return jsonify({"error": "No file part"}), 400
+    file = request.files["file"]
+    if file.filename == "":
+        return jsonify({"error": "No selected file"}), 400
+
+    try:
+        content = file.read().decode("utf-8", errors="ignore")
+        # Try to auto-detect delimiter; default ','
+        sniffer = csv.Sniffer()
+        dialect = None
+        try:
+            dialect = sniffer.sniff(content[:1024])
+        except Exception:
+            pass
+        reader = csv.DictReader(io.StringIO(
+            content), dialect=dialect) if dialect else csv.DictReader(io.StringIO(content))
+
+        required = {"name", "start_date", "end_date"}
+        if not required.issubset(set(h.lower() for h in reader.fieldnames or [])):
+            return jsonify({"error": "CSV must contain headers: name, start_date, end_date"}), 400
+
+        def parse_date(s: str):
+            s = (s or "").strip()
+            if not s:
+                return None
+            # Try ISO first
+            for fmt in ("%Y-%m-%d", "%d.%m.%Y", "%Y/%m/%d"):
+                try:
+                    return datetime.strptime(s, fmt).date()
+                except ValueError:
+                    continue
+            raise ValueError(f"Unsupported date format: {s}")
+
+        session = Session()
+        inserted = 0
+        updated = 0
+        for row in reader:
+            # Normalize headers to lower-case keys
+            norm = {k.lower(): (v or "").strip() for k, v in row.items()}
+            name = norm.get("name")
+            start_date = parse_date(norm.get("start_date"))
+            end_date = parse_date(norm.get("end_date"))
+            region = norm.get("region") or None
+            if not name or not start_date or not end_date:
+                continue
+
+            existing = (
+                session.query(SchoolHoliday)
+                .filter(
+                    SchoolHoliday.name == name,
+                    SchoolHoliday.start_date == start_date,
+                    SchoolHoliday.end_date == end_date,
+                    SchoolHoliday.region.is_(
+                        region) if region is None else SchoolHoliday.region == region,
+                )
+                .first()
+            )
+
+            if existing:
+                # Optionally update region or source_file_name
+                existing.region = region
+                existing.source_file_name = file.filename
+                updated += 1
+            else:
+                session.add(SchoolHoliday(
+                    name=name,
+                    start_date=start_date,
+                    end_date=end_date,
+                    region=region,
+                    source_file_name=file.filename,
+                ))
+                inserted += 1
+
+        session.commit()
+        session.close()
+        return jsonify({"success": True, "inserted": inserted, "updated": updated})
+    except Exception as e:
+        return jsonify({"error": str(e)}), 400