refactor: pure env_file stack.env convention across all stacks

Every service now reads stack.env via env_file with container-exact var
names — no ${VAR} parse-time interpolation, no Portainer UI env vars
(except stacks/dev, kept on UI-env interpolation as documented exception).

- media: drop PUID/PGID/TZ env lines (env_file covers); resolve ${ROOT}
- foundry: secrets via env_file; FOUNDRY_PATCH_URLS -> CONTAINER_PATCH_URLS
- monitoring: HOMARR_SECRET_ENCRYPTION_KEY -> SECRET_ENCRYPTION_KEY
- notify: FRESHRSS_USER composed in stack.env; TZ via env_file
- owncloud: container-exact OWNCLOUD_*/MYSQL_* keys; runtime $$ healthcheck
- resume/famapp: composites (DATABASE_URL etc.) written out in stack.env
- authentik: container-exact keys; image tag pinned in compose
- notes: couchdb creds via env_file
- remote: gains stack.env (no secrets; convention completeness)
- CLAUDE.md: env convention, valhalla-lab registration-only note, correct
  on-host Portainer working-copy path (/config/portainer/compose/<id>)

Validated with docker compose config on valhalla for all 15 stacks.

stacks/authentik/stack.env

@@ -1,6 +1,11 @@
-# authentik stack secrets
-AUTHENTIK_IMAGE_TAG=2024.12.3
-AUTHENTIK_DB_USER=authentik
-AUTHENTIK_DB_PASSWORD=ebb7d34ecbc4fc8f95cd16ef491d2162cdf8
-AUTHENTIK_DB_NAME=authentik
+# authentik stack secrets — injected into all services via env_file.
+# Var names are exactly what each container reads (no ${VAR} interpolation).
+# AUTHENTIK_POSTGRESQL__* (server/worker) and POSTGRES_* (db) must stay in sync.
+# Image tag is pinned in docker-compose.yml — bump it there via git.
+AUTHENTIK_POSTGRESQL__USER=authentik
+AUTHENTIK_POSTGRESQL__PASSWORD=ebb7d34ecbc4fc8f95cd16ef491d2162cdf8
+AUTHENTIK_POSTGRESQL__NAME=authentik
 AUTHENTIK_SECRET_KEY=C33S/oXOVOLrlLnWGMRYadgH9zfEC7Bm1vHtbczkFxHcTOj9j6io397c/OGb
+POSTGRES_USER=authentik
+POSTGRES_PASSWORD=ebb7d34ecbc4fc8f95cd16ef491d2162cdf8
+POSTGRES_DB=authentik