Add read-only Noya admin panel with assignments and UX polish.

Ship admin auth, user overview, assessments, chats, assignment filters/export, security hardening, and a separate desktop admin shell with clearer assessment answers.

Co-authored-by: Cursor <cursoragent@cursor.com>

backend/prisma/migrations/20260914170000_assignment_completion_rules/migration.sql

@@ -0,0 +1,8 @@
+-- Additive: completion threshold + per-day status for multi-day assignments.
+-- Non-destructive: existing rows keep requiresReport / draftData / entries unchanged.
+
+ALTER TABLE `assignment_definitions`
+  ADD COLUMN `minValidDays` INTEGER NULL;
+
+ALTER TABLE `assignment_daily_entries`
+  ADD COLUMN `dayStatus` ENUM('done', 'skipped', 'difficult') NOT NULL DEFAULT 'done';