feat: photos for tech tasks, 3 priorities, remove cleaning status from context menu

- Remove 'Убирается' (cleaning) from manually selectable HK statuses in calendar context menu — it now only shows automatically when a task is in_progress
- Reduce priorities from 4 to 3: remove 'high', keep urgent/medium/low across context menu, tech tasks modal, and HousekeepingTask type
- Add photo upload to technical tasks: upload via camera button per task, display thumbnails with hover-to-remove, stored as TEXT[] in DB (migration 026)
- Fix HousekeepingPage WS handler to filter by category — no longer adds maintenance tasks to housekeeping board
- Add 'tasks' folder support to upload route

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/migrations/026_task_photos.sql

@@ -0,0 +1,3 @@
+-- Add photos array to housekeeping_tasks
+ALTER TABLE housekeeping_tasks
+  ADD COLUMN IF NOT EXISTS photos TEXT[] NOT NULL DEFAULT '{}';