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

server/wsgi.py

@@ -3,6 +3,7 @@ from server.routes.eventmedia import eventmedia_bp
 from server.routes.files import files_bp
 from server.routes.events import events_bp
 from server.routes.holidays import holidays_bp
+from server.routes.academic_periods import academic_periods_bp
 from server.routes.groups import groups_bp
 from server.routes.clients import clients_bp
 from server.database import Session, engine
@@ -22,6 +23,7 @@ app.register_blueprint(events_bp)
 app.register_blueprint(eventmedia_bp)
 app.register_blueprint(files_bp)
 app.register_blueprint(holidays_bp)
+app.register_blueprint(academic_periods_bp)
 
 
 @app.route("/health")