feat(conversions): end-to-end PPT/PPTX/ODP -> PDF pipeline with RQ worker + Gotenberg

DB/model

Add Conversion model + ConversionStatus enum (pending, processing, ready, failed)
Alembic migrations: create conversions table, indexes, unique (source_event_media_id, target_format, file_hash), and NOT NULL on file_hash
API

Enqueue on upload (ppt|pptx|odp) in routes/eventmedia.py: compute sha256, upsert Conversion, enqueue job
New routes:
POST /api/conversions/<media_id>/pdf — ensure/enqueue conversion
GET /api/conversions/<media_id>/status — latest status/details
GET /api/files/converted/<path> — serve converted PDFs
Register conversions blueprint in wsgi
Worker

server/worker.py: convert_event_media_to_pdf
Calls Gotenberg /forms/libreoffice/convert, writes to server/media/converted/
Updates Conversion status, timestamps, error messages
Fix media root resolution to /server/media
Prefer function enqueue over string path; expose server.worker in package init for RQ string compatibility
Queue/infra

server/task_queue.py: RQ queue helper (REDIS_URL, default redis://redis:6379/0)
docker-compose:
Add redis and gotenberg services
Add worker service (rq worker conversions)
Pass REDIS_URL and GOTENBERG_URL to server/worker
Mount shared media volume in prod for API/worker parity
docker-compose.override:
Add dev redis/gotenberg/worker services
Ensure PYTHONPATH + working_dir allow importing server.worker
Use rq CLI instead of python -m rq for worker
Dashboard dev: run as appropriate user/root and pre-create/chown caches to avoid EACCES
Dashboard dev UX

Vite: set cacheDir .vite to avoid EACCES in node_modules
Disable Node inspector by default to avoid port conflicts
Docs

Update copilot-instructions.md with conversion system: flow, services, env vars, endpoints, storage paths, and data model

.github/copilot-instructions.md

@@ -23,12 +23,25 @@ Use this as your shared context when proposing changes. Keep edits minimal and m
   - Per-client group assignment (retained): `infoscreen/{uuid}/group_id` via `server/mqtt_helper.py`.
 - Screenshots: server-side folders `server/received_screenshots/` and `server/screenshots/`; Nginx exposes `/screenshots/{uuid}.jpg` via `server/wsgi.py` route.
 
+- Presentation conversion (PPT/PPTX/ODP → PDF):
+  - Trigger: on upload in `server/routes/eventmedia.py` for media types `ppt|pptx|odp` (compute sha256, upsert `Conversion`, enqueue job).
+  - Worker: RQ worker runs `server.worker.convert_event_media_to_pdf`, calls Gotenberg LibreOffice endpoint, writes to `server/media/converted/`.
+  - Services: Redis (queue) and Gotenberg added in compose; worker service consumes the `conversions` queue.
+  - Env: `REDIS_URL` (default `redis://redis:6379/0`), `GOTENBERG_URL` (default `http://gotenberg:3000`).
+  - Endpoints: `POST /api/conversions/<media_id>/pdf` (ensure/enqueue), `GET /api/conversions/<media_id>/status`, `GET /api/files/converted/<path>` (serve PDFs).
+  - Storage: originals under `server/media/…`, outputs under `server/media/converted/` (prod compose mounts a shared volume for this path).
+
 ## Data model highlights (see `models/models.py`)
 - Enums: `EventType` (presentation, website, video, message, webuntis), `MediaType` (file/website types), and `AcademicPeriodType` (schuljahr, semester, trimester).
 - Tables: `clients`, `client_groups`, `events`, `event_media`, `users`, `academic_periods`, `school_holidays`.
 - Academic periods: `academic_periods` table supports educational institution cycles (school years, semesters). Events and media can be optionally linked via `academic_period_id` (nullable for backward compatibility).
 - Times are stored as timezone-aware; treat comparisons in UTC (see scheduler and routes/events).
 
+- Conversions:
+  - Enum `ConversionStatus`: `pending`, `processing`, `ready`, `failed`.
+  - Table `conversions`: `id`, `source_event_media_id` (FK→`event_media.id` ondelete CASCADE), `target_format`, `target_path`, `status`, `file_hash` (sha256), `started_at`, `completed_at`, `error_message`.
+  - Indexes: `(source_event_media_id, target_format)`, `(status, target_format)`; Unique: `(source_event_media_id, target_format, file_hash)`.
+
 ## API patterns
 - Blueprints live in `server/routes/*` and are registered in `server/wsgi.py` with `/api/...` prefixes.
 - Session usage: instantiate `Session()` per request, commit when mutating, and always `session.close()` before returning.
@@ -51,6 +64,8 @@ Use this as your shared context when proposing changes. Keep edits minimal and m
    - Holidays present in the current view (count)
    - Period label (display_name or name) with a badge indicating whether any holidays exist in that period (overlap check)
 
+Note: Syncfusion usage in the dashboard is already documented above; if a UI for conversion status/downloads is added later, link its routes and components here.
+
 ## Local development
 - Compose: development is `docker-compose.yml` + `docker-compose.override.yml`.
   - API (dev): `server/Dockerfile.dev` with debugpy on 5678, Flask app `wsgi:app` on :8000.