fix: release v0.2.1 lesson deletes and large uploads

- Raise Traefik read timeout to 1h (compose dev/prod + k3s HelmChartConfig)
  so admin video uploads up to 200MB no longer 502 mid-upload.
- Migration 0029: cascade watch/quiz history on lesson delete and unlink
  dependent lessons, so removing a lesson or chapter stops 500ing.
- Add the Apollo cluster Helm overlay (values-apollo.yaml) for the deployed
  environment.
- k3s Traefik chart config also enables access logs, cross-namespace
  IngressRoutes, and fixes the Prometheus scrape port.

Bump appVersion/product.go/values tags to 0.2.1; chart version 0.2.3.

backend/internal/db/migrations/0029_lesson_delete_cascades.sql

@@ -0,0 +1,26 @@
+-- 0029_lesson_delete_cascades.sql
+-- Make deleting a lesson (directly, or via its chapter) work cleanly.
+--
+-- Previously only mcq_questions cascaded; watch/quiz history blocked the delete
+-- with a 500. Progress/history rows now go away with the lesson, while lessons
+-- that merely *required* the deleted one are unlinked (never deleted).
+
+ALTER TABLE watch_sessions DROP CONSTRAINT IF EXISTS watch_sessions_lesson_id_fkey;
+ALTER TABLE watch_sessions ADD CONSTRAINT watch_sessions_lesson_id_fkey
+    FOREIGN KEY (lesson_id) REFERENCES lessons(id) ON DELETE CASCADE;
+
+ALTER TABLE watch_heartbeats DROP CONSTRAINT IF EXISTS watch_heartbeats_lesson_id_fkey;
+ALTER TABLE watch_heartbeats ADD CONSTRAINT watch_heartbeats_lesson_id_fkey
+    FOREIGN KEY (lesson_id) REFERENCES lessons(id) ON DELETE CASCADE;
+
+ALTER TABLE lesson_progress DROP CONSTRAINT IF EXISTS lesson_progress_lesson_id_fkey;
+ALTER TABLE lesson_progress ADD CONSTRAINT lesson_progress_lesson_id_fkey
+    FOREIGN KEY (lesson_id) REFERENCES lessons(id) ON DELETE CASCADE;
+
+ALTER TABLE quiz_attempts DROP CONSTRAINT IF EXISTS quiz_attempts_lesson_id_fkey;
+ALTER TABLE quiz_attempts ADD CONSTRAINT quiz_attempts_lesson_id_fkey
+    FOREIGN KEY (lesson_id) REFERENCES lessons(id) ON DELETE CASCADE;
+
+ALTER TABLE lessons DROP CONSTRAINT IF EXISTS lessons_requires_lesson_id_fkey;
+ALTER TABLE lessons ADD CONSTRAINT lessons_requires_lesson_id_fkey
+    FOREIGN KEY (requires_lesson_id) REFERENCES lessons(id) ON DELETE SET NULL;