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

.github/copilot-instructions.md

@@ -16,6 +16,8 @@ It is not a changelog and not a full architecture handbook.
 - `scheduler/scheduler.py` - scheduler loop, MQTT event publishing, TV power intent publishing
 - `scheduler/db_utils.py` - event formatting and power-intent helper logic
 - `listener/listener.py` - discovery/heartbeat/log/screenshot MQTT consumption
+- `server/init_academic_periods.py` - idempotent academic-period seeding + auto-activation for current date
+- `server/initialize_database.py` - migration + bootstrap orchestration for local/manual setup
 - `server/routes/events.py` - event CRUD, recurrence handling, UTC normalization
 - `server/routes/eventmedia.py` - file manager, media upload/stream endpoints
 - `server/routes/groups.py` - group lifecycle, alive status, order persistence
@@ -32,6 +34,7 @@ It is not a changelog and not a full architecture handbook.
 - Listener: MQTT consumer that updates server-side state
 - Scheduler: publishes active events and group-level TV power intents
 - Nginx: routes `/api/*` and `/screenshots/*` to API, dashboard otherwise
+- Prod bootstrap: `docker-compose.prod.yml` server command runs migrations, defaults init, and academic-period init before Gunicorn start
 
 ## Non-negotiable conventions
 - Datetime:
@@ -66,12 +69,14 @@ TV power intent Phase 1 rules:
 - Keep enum/datetime serialization JSON-safe.
 - Maintain UTC-safe comparisons in scheduler and routes.
 - Keep recurrence handling backend-driven and consistent with exceptions.
+- Academic periods bootstrap is idempotent and should auto-activate period covering `date.today()` when available.
 
 ## Frontend patterns
 - Use Syncfusion-based patterns already present in dashboard.
 - Keep API requests relative (`/api/...`) to use Vite proxy in dev.
 - Respect `FRONTEND_DESIGN_RULES.md` for component and styling conventions.
 - Keep role-gated UI behavior aligned with backend authorization.
+- Holiday status banner in dashboard should render from computed state and avoid stale message reuse in 3rd-party UI components.
 
 ## Environment variables (high-value)
 - Scheduler: `POLL_INTERVAL_SECONDS`, `REFRESH_SECONDS`